Re: [PATCH v3 1/2] pwm: add microchip soft ip corePWM driver

[Conor.Dooley]

On 01/07/2022 10:51, Uwe Kleine-König wrote:
> Hello Conor,

Hey Uwe, thanks for the review!
I am on leave from work atm, doing my civic duty and all that so I don't
have a logic analyser on hand to do any testing with.

(comments I didn't reply to I agree with)
> 
> On Fri, Jun 17, 2022 at 12:44:42PM +0100, Conor Dooley wrote:
>> Add a driver that supports the Microchip FPGA "soft" PWM IP core.
>>
>> Signed-off-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
>> ---
>>  drivers/pwm/Kconfig              |  10 +
>>  drivers/pwm/Makefile             |   1 +
>>  drivers/pwm/pwm-microchip-core.c | 325 +++++++++++++++++++++++++++++++
>>  3 files changed, 336 insertions(+)
>>  create mode 100644 drivers/pwm/pwm-microchip-core.c
>>
>> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
>> index 21e3b05a5153..a651848e444b 100644
>> --- a/drivers/pwm/Kconfig
>> +++ b/drivers/pwm/Kconfig
>> @@ -383,6 +383,16 @@ config PWM_MEDIATEK
>>  	  To compile this driver as a module, choose M here: the module
>>  	  will be called pwm-mediatek.
>>  
>> +config PWM_MICROCHIP_CORE
>> +	tristate "Microchip corePWM PWM support"
>> +	depends on SOC_MICROCHIP_POLARFIRE || COMPILE_TEST
>> +	depends on HAS_IOMEM && OF
>> +	help
>> +	  PWM driver for Microchip FPGA soft IP core.
>> +
>> +	  To compile this driver as a module, choose M here: the module
>> +	  will be called pwm-microchip-core.
>> +
>>  config PWM_MXS
>>  	tristate "Freescale MXS PWM support"
>>  	depends on ARCH_MXS || COMPILE_TEST
>> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
>> index 708840b7fba8..d29754c20f91 100644
>> --- a/drivers/pwm/Makefile
>> +++ b/drivers/pwm/Makefile
>> @@ -33,6 +33,7 @@ obj-$(CONFIG_PWM_LPSS_PCI)	+= pwm-lpss-pci.o
>>  obj-$(CONFIG_PWM_LPSS_PLATFORM)	+= pwm-lpss-platform.o
>>  obj-$(CONFIG_PWM_MESON)		+= pwm-meson.o
>>  obj-$(CONFIG_PWM_MEDIATEK)	+= pwm-mediatek.o
>> +obj-$(CONFIG_PWM_MICROCHIP_CORE)	+= pwm-microchip-core.o
>>  obj-$(CONFIG_PWM_MTK_DISP)	+= pwm-mtk-disp.o
>>  obj-$(CONFIG_PWM_MXS)		+= pwm-mxs.o
>>  obj-$(CONFIG_PWM_NTXEC)		+= pwm-ntxec.o
>> diff --git a/drivers/pwm/pwm-microchip-core.c b/drivers/pwm/pwm-microchip-core.c
>> new file mode 100644
>> index 000000000000..abbfc1cd23c4
>> --- /dev/null
>> +++ b/drivers/pwm/pwm-microchip-core.c
>> @@ -0,0 +1,325 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * corePWM driver for Microchip "soft" FPGA IP cores.
>> + *
>> + * Copyright (c) 2021-2022 Microchip Corporation. All rights reserved.
>> + * Author: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
>> + * Documentation:
>> + * https://www.microsemi.com/document-portal/doc_download/1245275-corepwm-hb
>> + *
>> + * Limitations:
>> + * - If the IP block is configured without "shadow registers", all register
>> + *   writes will take effect immediately, causing glitches on the output.
>> + *   If shadow registers *are* enabled, a write to the "SYNC_UPDATE" register
>> + *   notifies the core that it needs to update the registers defining the
>> + *   waveform from the contents of the "shadow registers".
>> + * - The IP block has no concept of a duty cycle, only rising/falling edges of
>> + *   the waveform. Unfortunately, if the rising & falling edges registers have
>> + *   the same value written to them the IP block will do whichever of a rising
>> + *   or a falling edge is possible. I.E. a 50% waveform at twice the requested
>> + *   period. Therefore to get a 0% waveform, the output is set the max high/low
>> + *   time depending on polarity.
> 
> Ah, that behaviour explains how the hardware works. The logic is:
> 
> 	if $currently_high:
> 	    if $clkcnt = $negedge:
> 	        set(low)
> 	else:
> 	    if $clkcnt = $posedge:
> 	        set(high)

I am just going to ask for the rtl when I get a chance I think.

 
> The same problem exists for 100% relative duty cycle, doesn't it?
> 
> How does the PWM behave with:
> 
> 	PERIOD = 0xfe
> 	POSEDGE = 0xff
> 	NEGEDGE = 0
> 
> I assume this yields constant low output.

This specific combo I have not tested, but afaik yes.

How does that change if you set
> PERIOD = 0xff? If the output isn't constant low then, maybe that's a
> reason to not permit PERIOD = 0xff.
> 
> Below you configure for duty_cycle = 0:
> 
> 	POSEDGE = PERIOD
> 	NEGEDGE = 0
> 
> In my understanding this doesn't result in a constant output?!

Hopefully the RTL will help me clear this up. I switched the code
to this because of the 50% thing mentioned above. In testing it,
I could not get my scope to trigger on the output for a range of
periods. But that does not really make very much sense looking at
the code now.

At the moment, a /PERIOD/ of 0xE (so a reg value of 0xD) will count
0x0 -> 0xD and then roll over to 0x0. 

posedge (the register value) is being set to 0xD not 0xE, so this
should not be a constant output. I think what must have happened
is that I had been using the variable "period_steps" to be the
real number of steps during my development/testing of V3. But when
I, at the very end, was testing with shadow register enabled I
found an idempotency issue. I had attempted to remove the
period_steps & prescale args to mchp_core_pwm_apply_duty() and just
read them locally - but with shadow registers enabled the reg values
visible on the bus were the old values so the calculation was wrong
in cases where the period was changing.

When I readded them to the signature, I renamed the real period_steps
value to period_steps_val & must not have updated or properly tested
the 0/100% duty cycles. Bleh.

Not 100% on this, but fairly sure that this is the case. Sorry.

> 
>> + * - The PWM period is set for the whole IP block not per channel. The driver
>> + *   will only change the period if no other PWM output is enabled.
>> + */
>> +
>> +#include <linux/clk.h>
>> +#include <linux/delay.h>
>> +#include <linux/err.h>
>> +#include <linux/io.h>
>> +#include <linux/module.h>
>> +#include <linux/of_device.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/pwm.h>
>> +#include <linux/math.h>
>> +
>> +#define PREG_TO_VAL(PREG) ((PREG) + 1)
>> +
>> +#define COREPWM_PRESCALE_REG	0x00u
>> +#define COREPWM_PERIOD_REG	0x04u
>> +#define COREPWM_EN_LOW_REG	0x08u
>> +#define COREPWM_EN_HIGH_REG	0x0Cu
>> +#define COREPWM_SYNC_UPD_REG	0xE4u
>> +#define COREPWM_POSEDGE_OFFSET	0x10u
>> +#define COREPWM_NEGEDGE_OFFSET	0x14u
>> +#define COREPWM_CHANNEL_OFFSET	0x08u
> 
> I'd define the registers as follows:
> 
> 	#define MCHPCOREPWM_PRESCALE		0x00
> 	#define MCHPCOREPWM_PERIOD		0x04
> 	#define MCHPCOREPWM_EN(i)		(0x08 + 0x04 * (i)) /* 0x08, 0x0c */
> 	#define MCHPCOREPWM_POSEDGE(i)		(0x10 + 0x08 * (i)) /* 0x10, 0x18, ..., 0x88 */
> 	#define MCHPCOREPWM_NEGEDGE(i)		(0x14 + 0x08 * (i)) /* 0x14, 0x1c, ..., 0x8c */
> 	#define MCHPCOREPWM_SYNC_UPD		0xe4
> 
> This is IMHO a bit better to understand and simplifies usage.

Sure.

> 
>> +
>> +struct mchp_core_pwm_chip {
>> +	struct pwm_chip chip;
>> +	struct clk *clk;
>> +	void __iomem *base;
>> +	u32 sync_update_mask;
>> +};
>> +
>> +static inline struct mchp_core_pwm_chip *to_mchp_core_pwm(struct pwm_chip *chip)
>> +{
>> +	return container_of(chip, struct mchp_core_pwm_chip, chip);
>> +}
>> +
>> +static void mchp_core_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm, bool enable)
>> +{
>> +	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
>> +	u8 channel_enable, reg_offset, shift;
>> +
>> +	/*
>> +	 * There are two adjacent 8 bit control regs, the lower reg controls
>> +	 * 0-7 and the upper reg 8-15. Check if the pwm is in the upper reg
>> +	 * and if so, offset by the bus width.
>> +	 */
>> +	reg_offset = COREPWM_EN_LOW_REG + (pwm->hwpwm >> 3) * sizeof(u32);
>> +	shift = pwm->hwpwm > 7 ? pwm->hwpwm - 8 : pwm->hwpwm;
>> +
>> +	channel_enable = readb_relaxed(mchp_core_pwm->base + reg_offset);
>> +	channel_enable &= ~(1 << shift);
>> +	channel_enable |= (enable << shift);
>> +
>> +	writel_relaxed(channel_enable, mchp_core_pwm->base + reg_offset);
>> +
>> +	/*
>> +	 * Write to the sync update registers so that channels with shadow
>> +	 * registers will also get their enable update. This operation is a NOP
>> +	 * for channels without shadow registers.
>> +	 */
>> +	writel_relaxed(1U, mchp_core_pwm->base + COREPWM_SYNC_UPD_REG);
> 
> Hmmmmm, this is racy. Consider there are two PWMs in use and two
> pwm_apply calls are run in parallel. Then the sync update in the first
> execution thread triggers an update for the second which might just be
> in the middle of updating registers and so there is a glitch for the 2nd
> PWM. So this needs locking to behave correctly.

Yeah, SGTM.

> 
>> +}
>> +
>> +static void mchp_core_pwm_apply_duty(struct pwm_chip *chip, struct pwm_device *pwm,
>> +				     const struct pwm_state *state, u8 prescale, u8 period_steps)
>> +{
>> +	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
>> +	void __iomem *channel_base = mchp_core_pwm->base + pwm->hwpwm * COREPWM_CHANNEL_OFFSET;
>> +	u64 duty_steps, period, tmp;
>> +	u8 posedge, negedge;
>> +	u8 prescale_val = PREG_TO_VAL(prescale);
> 
> If prescale is 0xff we get prescale_val = 0 which is bogus.

"yes"
> 
>> +	u8 period_steps_val = PREG_TO_VAL(period_steps);
>> +
>> +	period = period_steps_val * prescale_val * NSEC_PER_SEC;
>> +	period = div64_u64(period, clk_get_rate(mchp_core_pwm->clk));
> 
> You need to round up here.
> 
>> +	/*
>> +	 * Calculate the duty cycle in multiples of the prescaled period:
>> +	 * duty_steps = duty_in_ns / step_in_ns
>> +	 * step_in_ns = (prescale * NSEC_PER_SEC) / clk_rate
>> +	 * The code below is rearranged slightly to only divide once.
>> +	 *
>> +	 * Because the period is per channel, it is possible that the requested
>> +	 * duty cycle is longer than the period, in which case cap it to the
>> +	 * period.
>> +	 */
>> +	if (state->duty_cycle > period) {
>> +		duty_steps = period_steps;
>> +	} else {
>> +		duty_steps = state->duty_cycle * clk_get_rate(mchp_core_pwm->clk);
>> +		tmp = prescale_val * NSEC_PER_SEC;
>> +		duty_steps = div64_u64(duty_steps, tmp);
>> +	}
>> +
>> +	/*
>> +	 * Turn the output on unless posedge == negedge, in which case the
>> +	 * duty is intended to be 0, but limitations of the IP block don't
>> +	 * allow a zero length duty cycle - so just set the max high/low time
>> +	 * respectively.
>> +	 */
>> +	if (state->polarity == PWM_POLARITY_INVERSED) {
>> +		negedge = !duty_steps ? period_steps : 0u;
>> +		posedge = duty_steps;
>> +	} else {
>> +		posedge = !duty_steps ? period_steps : 0u;
>> +		negedge = duty_steps;
>> +	}
>> +
>> +	writel_relaxed(posedge, channel_base + COREPWM_POSEDGE_OFFSET);
>> +	writel_relaxed(negedge, channel_base + COREPWM_NEGEDGE_OFFSET);
>> +}
>> +
>> +static void mchp_core_pwm_apply_period(struct pwm_chip *chip, const struct pwm_state *state,
>> +				       u8 *prescale, u8 *period_steps)
>> +{
>> +	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
>> +	u64 tmp = state->period;
>> +
>> +	/*
>> +	 * Calculate the period cycles and prescale values.
>> +	 * The registers are each 8 bits wide & multiplied to compute the period
>> +	 * so the maximum period that can be generated is 0xFFFF times the period
> 
> 0xff * 0xff != 0xffff

Gah.. That was silly of me.
(0xff + 0x1)^2 is the correct max as the period calculation is:
(clock_period) * (prescale_reg + 1) * (period_reg + 1)
Still wrong but less wrong than 0xff * 0xff I guess.

> 
>> +	 * of the input clock.
>> +	 */
>> +	tmp *= clk_get_rate(mchp_core_pwm->clk);
> 
> This might overflow. Better use mul_u64_u64_div_u64 and require

mul_u64_u64_div_u64(), what a mouthful haha.
willdo.

> clk_get_rate(mchp_core_pwm->clk) < NSEC_PER_SEC.
> 
>> +	do_div(tmp, NSEC_PER_SEC);
>> +
>> +	if (tmp > 0xFFFFu) {
>> +		*prescale = 0xFFu;
>> +		*period_steps = 0xFFu;
>> +	} else {
>> +		*prescale = tmp >> 8;
>> +		do_div(tmp, PREG_TO_VAL(*prescale));
>> +		*period_steps = tmp - 1;
>> +	}
> 
> The goal here is to determine prescale and period_steps such that (in
> order of importance):
> 
>  a) Both are in [0, 255]
>  b) (prescale + 1) * (period_steps + 1) <= tmp
>  c) (prescale + 1) * (period_steps + 1) should be big
>  d) period_steps should be big[1]
> 
> (If it simplifies the implementation you can also put d) above c))> 
> So there are a few things to improve here. For example with tmp = 0xfffe
> you get prescale = 0xff + period_steps = 0xfe which violates d)

Aight, I'll take another look at optimising this so.


> 
> [1] In most cases this is beneficial as a big period_steps value allows
>     a more finegrained selection for duty_cycle.
> 
>> +	writel_relaxed(*prescale, mchp_core_pwm->base + COREPWM_PRESCALE_REG);
>> +	writel_relaxed(*period_steps, mchp_core_pwm->base + COREPWM_PERIOD_REG);
>> +}
>> +
>> +static int mchp_core_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>> +			       const struct pwm_state *state)
>> +{
>> +	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
>> +	struct pwm_state current_state = pwm->state;
>> +	bool period_locked;
>> +	u16 channel_enabled;
>> +	u8 prescale, period_steps;
>> +
>> +	if (!state->enabled) {
>> +		mchp_core_pwm_enable(chip, pwm, false);
>> +		return 0;
>> +	}
>> +
>> +	/*
>> +	 * If the only thing that has changed is the duty cycle or the polarity,
>> +	 * we can shortcut the calculations and just compute/apply the new duty
>> +	 * cycle pos & neg edges
>> +	 * As all the channels share the same period, do not allow it to be
>> +	 * changed if any other channels are enabled.
>> +	 */
>> +	channel_enabled = (((u16)readb_relaxed(mchp_core_pwm->base + COREPWM_EN_HIGH_REG) << 8) |
>> +		readb_relaxed(mchp_core_pwm->base + COREPWM_EN_LOW_REG));
> 
> The bits 15:8 of COREPWM_EN_LOW_REG are always zero I assume?

Yeah

> 
>> +	period_locked = channel_enabled & ~(1 << pwm->hwpwm);
> 
> This is racy, too.
> 
>> +	if ((!current_state.enabled || current_state.period != state->period) && !period_locked) {
>> +		mchp_core_pwm_apply_period(chip, state, &prescale, &period_steps);
>> +	} else {
>> +		prescale = readb_relaxed(mchp_core_pwm->base + COREPWM_PRESCALE_REG);
>> +		period_steps = readb_relaxed(mchp_core_pwm->base + COREPWM_PERIOD_REG);
>> +	}
> 
> If the configured period is bigger than the requested one, you should
> return -EINVAL.

Cool, willdo.

> 
>> +	mchp_core_pwm_apply_duty(chip, pwm, state, prescale, period_steps);
>> +
>> +	/*
>> +	 * Notify the block to update the waveform from the shadow registers.
>> +	 * The updated values will not appear on the bus until they have been
>> +	 * applied to the waveform at the beginning of the next period.
>> +	 */
>> +	if (mchp_core_pwm->sync_update_mask & (1 << pwm->hwpwm)) {
>> +		writel_relaxed(1U, mchp_core_pwm->base + COREPWM_SYNC_UPD_REG);
>> +		usleep_range(state->period, state->period * 2);
>> +	}
>> +
>> +	mchp_core_pwm_enable(chip, pwm, true);
> 
> mchp_core_pwm_enable writes the COREPWM_SYNC_UPD_REG register, too. Do
> you really need to write it twice?

Yeah, good point.

> 
>> +	return 0;
>> +}
>> +
>> +static void mchp_core_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
>> +				    struct pwm_state *state)
>> +{
>> +	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
>> +	void __iomem *channel_base = mchp_core_pwm->base + pwm->hwpwm * COREPWM_CHANNEL_OFFSET;
>> +	u8 prescale, period_steps, duty_steps;
>> +	u8 posedge, negedge;
>> +	u16 channel_enabled;
>> +
>> +	channel_enabled = (((u16)readb_relaxed(mchp_core_pwm->base + COREPWM_EN_HIGH_REG) << 8) |
>> +		readb_relaxed(mchp_core_pwm->base + COREPWM_EN_LOW_REG));
>> +
>> +	if (channel_enabled & 1 << pwm->hwpwm)
>> +		state->enabled = true;
>> +	else
>> +		state->enabled = false;
>> +
>> +	prescale = PREG_TO_VAL(readb_relaxed(mchp_core_pwm->base + COREPWM_PRESCALE_REG));
>> +
>> +	posedge = readb_relaxed(channel_base + COREPWM_POSEDGE_OFFSET);
>> +	negedge = readb_relaxed(channel_base + COREPWM_NEGEDGE_OFFSET);
>> +
>> +	duty_steps = abs((s16)posedge - (s16)negedge);
>> +	state->duty_cycle = duty_steps * prescale * NSEC_PER_SEC;
>> +	do_div(state->duty_cycle, clk_get_rate(mchp_core_pwm->clk));
>> +
>> +	state->polarity = negedge < posedge ? PWM_POLARITY_INVERSED : PWM_POLARITY_NORMAL;
>> +
>> +	period_steps = PREG_TO_VAL(readb_relaxed(mchp_core_pwm->base + COREPWM_PERIOD_REG));
>> +	state->period = period_steps * prescale * NSEC_PER_SEC;
>> +	do_div(state->period, clk_get_rate(mchp_core_pwm->clk));
>> +}
>> +
>> +static const struct pwm_ops mchp_core_pwm_ops = {
>> +	.apply = mchp_core_pwm_apply,
>> +	.get_state = mchp_core_pwm_get_state,
>> +	.owner = THIS_MODULE,
>> +};
>> +
>> +static const struct of_device_id mchp_core_of_match[] = {
>> +	{
>> +		.compatible = "microchip,corepwm-rtl-v4",
>> +	},
>> +	{ /* sentinel */ }
>> +};
>> +MODULE_DEVICE_TABLE(of, mchp_core_of_match);
>> +
>> +static int mchp_core_pwm_probe(struct platform_device *pdev)
>> +{
>> +	struct mchp_core_pwm_chip *mchp_pwm;
>> +	struct resource *regs;
>> +	int ret;
>> +
>> +	mchp_pwm = devm_kzalloc(&pdev->dev, sizeof(*mchp_pwm), GFP_KERNEL);
>> +	if (!mchp_pwm)
>> +		return -ENOMEM;
>> +
>> +	mchp_pwm->base = devm_platform_get_and_ioremap_resource(pdev, 0, &regs);
>> +	if (IS_ERR(mchp_pwm->base))
>> +		return PTR_ERR(mchp_pwm->base);
>> +
>> +	mchp_pwm->clk = devm_clk_get(&pdev->dev, NULL);
>> +	if (IS_ERR(mchp_pwm->clk))
>> +		return PTR_ERR(mchp_pwm->clk);
>> +
>> +	if (of_property_read_u32(pdev->dev.of_node, "microchip,sync-update-mask",
>> +				 &mchp_pwm->sync_update_mask))
>> +		mchp_pwm->sync_update_mask = 0u;
>> +
>> +	ret = clk_prepare_enable(mchp_pwm->clk);
>> +	if (ret)
>> +		return dev_err_probe(&pdev->dev, ret, "failed to prepare PWM clock\n");
>> +
>> +	mchp_pwm->chip.dev = &pdev->dev;
>> +	mchp_pwm->chip.ops = &mchp_core_pwm_ops;
>> +	mchp_pwm->chip.of_xlate = of_pwm_xlate_with_flags;
>> +	mchp_pwm->chip.of_pwm_n_cells = 3;
> 
> You can drop these two, assuming you have #pwm-cells = <3> in the dtb,
> they are also assigned by the core like that. (And if you don't it's
> ugly to assign these and you're better of the the stuff that the pwm
> core does.)

The dts actually says 2 at the moment so that needs fixing..

> 
>> +	mchp_pwm->chip.npwm = 16;
>> +
>> +	ret = pwmchip_add(&mchp_pwm->chip);
>> +	if (ret < 0) {
>> +		clk_disable_unprepare(mchp_pwm->clk);
>> +		return dev_err_probe(&pdev->dev, ret, "failed to add PWM chip\n");
>> +	}
>> +
>> +	platform_set_drvdata(pdev, mchp_pwm);
>> +	dev_info(&pdev->dev, "Successfully registered Microchip corePWM\n");
> 
> I recommend to drop this message. If every driver does that, you get
> quite a lot of messages that are not very helpful (once development of
> the driver is done) and delay the boot up time.

My CI likes them, but if you don't - I am happy to drop it.

> 
>> +	return 0;
>> +}
>> +
>> +static int mchp_core_pwm_remove(struct platform_device *pdev)
>> +{
>> +	struct mchp_core_pwm_chip *mchp_pwm = platform_get_drvdata(pdev);
>> +
>> +	pwmchip_remove(&mchp_pwm->chip);
>> +	clk_disable_unprepare(mchp_pwm->clk);
> 
> If you use devm_clk_get_enabled() and devm_pwmchip_add() in .probe(),
> you can drop .remove()

SGTM

> 
>> +
>> +	return 0;
>> +}
>> +
>> +static struct platform_driver mchp_core_pwm_driver = {
>> +	.driver = {
>> +		.name = "mchp-core-pwm",
>> +		.of_match_table = mchp_core_of_match,
>> +	},
>> +	.probe = mchp_core_pwm_probe,
>> +	.remove = mchp_core_pwm_remove,
>> +};
>> +module_platform_driver(mchp_core_pwm_driver);
>> +
>> +MODULE_LICENSE("GPL");
>> +MODULE_AUTHOR("Conor Dooley <conor.dooley@xxxxxxxxxxxxx>");
>> +MODULE_DESCRIPTION("corePWM driver for Microchip FPGAs");
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/linux-riscv