Re: [PATCH V2] clk: tegra: initialise parent of uart clocks

From: Laxman Dewangan
Date: Thu Feb 14 2013 - 05:51:31 EST

On Wednesday 13 February 2013 10:04 PM, Stephen Warren wrote:
On 02/13/2013 12:02 AM, Laxman Dewangan wrote:
On Tuesday 12 February 2013 11:16 PM, Stephen Warren wrote:
On 02/12/2013 08:17 AM, Laxman Dewangan wrote:
Initialise the parent of UARTs to PLLP and disabling clock by
This patch wasn't tested, was it? Without the patch I just sent titled
"ARM: tegra: remove clock-frequency properties from serial nodes", the
UART clocks get turned off and the console breaks.
I tested this in next-20130212 where "clock-frequency" is there in
tegra30.dtsi file.
I tested on Cardhu/Tegra30 (I'd previously only tested on
Harmony/Tegra20), and I see the exact same problem; the clock core turns
off the UART clock and the system hangs.

Are you sure you don't have any other local patches that somehow keep
the UART clock on (e.g. disabling clk_disable_unused, calling clk_get()
on the UART clock somewhere else, have the Tegra HS UART driver enabled
on the console port for testing which perhaps does an unconditional
clk_get). Are you sure you're testing with U-Boot rather than our binary
bootloader; who knows what kind of voodoo that does to clocks.

Note: I tested: a merge of arm-soc/for-next and Tegra's for-next branch,
with my patch to remove the clock-frequency properties reverted, plus a
fix for the boot crash ("clockevents: fix generic broadcast for

If you remove this from dts file at all then it will not work as there
is no execution path to call the clk_prepare_enable().

of_serial.c file:
if (of_property_read_u32(np, "clock-frequency", &clk)) {
That returns 0 if the property is present (so doesn't get/enable the
clock), and an error code if the property is missing (so does get/enable
the clock).

Ahha..Yes, got it. I tested this in next-20130212 with the maintainer's patch for broadcast, reverting one change "OF: convert devtree lock from rw_lock to raw spinlock" and
uart clock change. The system was booting but not reaching to login. I was assumign that it may be the issue with other reason as I saw the uart log.

After taking your patch for removing clock-freq and this patch, the system booted to login prompt means it is working fine.

So I was wrong when telling clock-frequency is required. Actually it should not be to work properly.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at