Re: [PATCH 2/2] mmc: dw_mmc: add resets support to dw_mmc

[zhangfei]

On 03/30/2016 08:46 AM, Shawn Lin wrote:
> å 2016/3/29 16:23, zhangfei åé:

> > > More to think, Is it ok to match the behaviour of bootloader stage?
> > > My bootloader doesn't assert the reset pin of dw_mmc, so it seams if
> > > I want to fix you issue on kernel stage, I need a new round of
> > > assert->delay->deassert.
> >
> > The process like delay (if required) should be abstracted in reset
> > driver.
> > reset framework just export reset_control_assert/reset_control_deassert
> > API.
> > Unfortunately not find clear description in Documentation/.
> > Suppose deassert is like start, while assert is like stop.
>
> yes, no docs except dt-bindings..... So seems the usage of these two
> APIs depends on the implementation of reset controller driver
>
> > drivers/reset/core.c
> > reset_control_deassert - deasserts the reset line
> > reset_control_assert - asserts the reset line
> >
> > More example:
> > drivers/mmc/host/sdhci-st.c
> > drivers/mmc/host/sunxi-mmc.c
> > drivers/usb/host/ohci-platform.c
> > drivers/i2c/busses/i2c-mv64xxx.c
>
> But I'm afraid I have to nack here....
>
> Looking at these files:
> drivers/dma/stm32-dma.c
> drivers/net/ethernet/mediatek/mtk_eth_soc.c
> drivers/devfreq/tegra-devfreq.c
> drivers/crypto/rockchip/rk3288_crypto.c
> drivers/thermal/rockchip_thermal.c
> drivers/thermal/tegra_soctherm.c
> drivers/i2c/busses/i2c-tegra.c
> ....
>
> they just do the way like: assert->[delay](maybe abstracted)->deassert
> I think these drivers are vendor specific, so they can do
> the reset operations in consistent with the implementation of
> their platforms' reset controller drivers.

Yes, have checked drivers/i2c/busses/i2c-tegra.c
        reset_control_assert(i2c_dev->rst);
        udelay(2);
        reset_control_deassert(i2c_dev->rst);

This usage looks strange, reset does not mean gpio reset, it maybe 
register accessing.
I think all these three operation should be abstracted to deassert 
function, while cover the details for sharing.

However, not doc describing the assert/deassert behavior so causing 
confusion.

> But, dw_mmc is shared by many Socs. So It's not good to do it in
> dw_mci_probe, otherwise you force my reset controller driver to be
> implemented in the same way as yours..... Right?
>
> How about move it to your drv_data->init callback?
Yes, we can.
But firstly we should consider put in common file for sharing, otherwise 
there maybe many assert/deassert in dw_mmc-xx.c.

Guodong may send another version and wait for Jaehoon's decision.

Thanks