[PATCH v2] clk: exynos5420: Keep aclk66_peric enabled during boot
tomasz.figa at gmail.com
Thu Jun 5 12:31:53 PDT 2014
On 05.06.2014 21:22, Doug Anderson wrote:
> On Thu, Jun 5, 2014 at 12:14 PM, Tomasz Figa <tomasz.figa at gmail.com> wrote:
>> On 05.06.2014 20:48, Doug Anderson wrote:
>>> Tomasz / Mike,
>>> On Fri, May 30, 2014 at 9:32 AM, Doug Anderson <dianders at chromium.org> wrote:
>>>> Right now if you've got earlyprintk enabled on exynos5420-peach-pit
>>>> then you'll get a hang on boot. Here's why:
>>>> 1. The i2c-s3c2410 driver will probe at subsys_initcall. It will
>>>> enable its clock and disable it. This is the clock "i2c2".
>>>> 2. The act of disabling "i2c2" will disable its parents. In this case
>>>> the parent is "aclk66_peric". There are no other children of
>>>> "aclk66_peric" officially enabled, so "aclk66_peric" will be turned
>>>> off (despite being CLK_IGNORE_UNUSED, but that's by design).
>>>> 3. The next time you try to earlyprintk you'll do so without the UART
>>>> clock enabled. That's because the UART clocks are also children of
>>>> "aclk66_peric". You'll hang.
>>>> There's no good place to put a clock enable for earlyprintk, which is
>>>> handled by a bunch of assembly code. The best we can do is to handle
>>>> this in the clock driver.
>>>> Signed-off-by: Doug Anderson <dianders at chromium.org>
>>>> Tested-by: Javier Martinez Canillas <javier.martinez at collabora.co.uk>
>>>> Changes in v2:
>>>> - Use GATE_A and clk_get(). Save the clock for putting later.
>>>> - Return 0 from exynos5420_clk_late_init().
>>>> drivers/clk/samsung/clk-exynos5420.c | 33 +++++++++++++++++++++++++++++++--
>>>> 1 file changed, 31 insertions(+), 2 deletions(-)
>>> Are there other changes you'd like me to make to this? It would be
>>> really nice to get this in for 3.16 so the system doesn't just
>>> mysteriously hang when you use earlyprintk.
>> We can probably take this as an -rc fix, so it should be fine.
>> However I still don't see the point of exporting this clock and
>> polluting the global clkdev namespace. Even the diffstat looks better in v1.
> OK, I'm happy to go back to v1 with the addition of the "return 0".
> Mike: are you OK with that?
One more question that just came to my mind: Why it is just the
aclk66_peri and not its children related to UARTs?
Exynos5420 clock driver still needs a little clean-up, so I'm okay with
any fix for now and changing this later if needed, but is this gate
clock for ACLK66_PERIC even needed? It seems to be marked with
CLK_IGNORE_UNUSED which suggests that it is not needed in this driver at
all, along with other similar clocks. AFAIK for power management
purposes our fine-grained approach is fine and we shouldn't need to use
the big gates.
More information about the linux-arm-kernel