[PATCH v2 2/4] mmc: sdhci-brcmstb: Enable Clock Gating to save power

[Florian Fainelli]

On 4/27/22 14:39, Ulf Hansson wrote:
> On Wed, 27 Apr 2022 at 20:09, Kamal Dasu <kdasu.kdev at gmail.com> wrote:
>>
>> From: Al Cooper <alcooperx at gmail.com>
>>
>> Enabling this feature will allow the controller to stop the bus
>> clock when the bus is idle. The feature is not part of the standard
>> and is unique to newer Arasan cores and is enabled with a bit in a
>> vendor specific register. This feature will only be enabled for
>> non-removable devices because they don't switch the voltage and
>> clock gating breaks SD Card volatge switching.
> 
> Rather than using a HW specific thing for this, it may be better to
> use runtime PM. There are plenty of examples to get inspired from, so
> it should be rather easy to implement, I think. More importantly, it
> should work for both (e)MMC and SD cards, unless there are some
> specific things to manage for this controller.
> 
> When it comes to SDIO, some driver simply bumps the runtime PM usage
> count (pm_runtime_get_noresume()) to prevent the device from being
> runtime suspended. There are ways to work around this, let me know if
> you need some guidance around how to fix that too.
> 
> That said, I am not entirely opposed to $subject patch, but I wanted
> to point out that there are better alternatives.

This is a good suggestion, I would not consider runtime PM and enabling 
the clock gating as being alternatives to one another, but rather 
complementary.
-- 
Florian