[PATCH v5 1/6] pwms: pwm-ti*: Get the clock from the PWMSS (parent)
nsekhar at ti.com
Mon Apr 11 04:49:37 PDT 2016
On Monday 11 April 2016 02:21 AM, Paul Walmsley wrote:
> Hi guys
> On Tue, 5 Apr 2016, Franklin S Cooper Jr. wrote:
>> On 04/05/2016 01:08 AM, Sekhar Nori wrote:
>>> On Tuesday 08 March 2016 06:53 AM, Franklin S Cooper Jr wrote:
>>>> The eCAP and ePWM doesn't have their own separate clocks. They simply
>>>> utilize the clock provided directly by the PWMSS. Therefore, they simply
>>>> need to grab a reference to their parent's clock.
>>>> Signed-off-by: Franklin S Cooper Jr <fcooper at ti.com>
>>> So this assumes that eCAP and eHRPWM are always under the PWMSS
>>> umbrella. But on TI AM18x, thats not true. These IPs exist independently
>>> and receive functional clock from PLL sysclk outputs.
>>>> drivers/pwm/pwm-tiecap.c | 2 +-
>>>> drivers/pwm/pwm-tiehrpwm.c | 2 +-
>>>> 2 files changed, 2 insertions(+), 2 deletions(-)
>>>> diff --git a/drivers/pwm/pwm-tiecap.c b/drivers/pwm/pwm-tiecap.c
>>>> index 616af76..9418159 100644
>>>> --- a/drivers/pwm/pwm-tiecap.c
>>>> +++ b/drivers/pwm/pwm-tiecap.c
>>>> @@ -212,7 +212,7 @@ static int ecap_pwm_probe(struct platform_device *pdev)
>>>> if (!pc)
>>>> return -ENOMEM;
>>>> - clk = devm_clk_get(&pdev->dev, "fck");
>>>> + clk = devm_clk_get(pdev->dev.parent, "fck");
>>> Even keeping the AM18x usecase aside, this seems to be pushing too much
>>> platform information into the driver. The "fck" is a valid connection id
>>> for the eCAP IP. Whether its valid for the parent device too is not
>>> something this driver should need to know.
>>> So it looks like what you need is for the clock hierarchy for the
>>> platform to have clocks for eHRPWM and eCAP derived out of PWMSS clock?
>> So I believe this is a question on if we want to hide the minor
>> delta between AM18 vs AM335x, AM437x and AM57x/DRA7 in the driver
>> or within the DT.
>> Note that handling this by defining new clocks in DT will then
>> result in older DTBs not working. I don't think its worth breaking
>> backwards compatibility for AM335x and AM437x DTBs for fixing support
>> for AM18 based SOCs. Especially since those SOCs haven't worked with
>> this driver for several years. By handling things within the driver rather
>> than DT we can atleast insure that we can get everything working while
>> avoiding breaking backwards compatibility.
> I agree with Sekhar that we shouldn't embed this parent clock quirk
> into the driver.
> Can you just define a new compatibility string such that the driver can be
> written with no embedded integration quirks? Then add a workaround in the
> driver that will use pdev->dev.parent for the old (deprecated)
> compatibility string and log a warning to the kernel console that the DT
> needs to be updated.
Thanks Paul! Although not sure if adding a new compatible for the IP is
the best way (since that would denote a different version of the IP).
How about checking for parent clock iff clk_get() on own device fails
and of_machine_is_compatible() matches the platforms where backward
compatibility needs to be maintained?
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