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From: Florian Fainelli <f.fainelli@gmail.com>
To: Ulf Hansson <ulf.hansson@linaro.org>, Kamal Dasu <kdasu.kdev@gmail.com>
Cc: robh+dt@kernel.org, krzk+dt@kernel.org, alcooperx@gmail.com,
	bcm-kernel-feedback-list@broadcom.com, adrian.hunter@intel.com,
	linux-mmc@vger.kernel.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 2/4] mmc: sdhci-brcmstb: Enable Clock Gating to save power
Date: Wed, 27 Apr 2022 14:43:46 -0700	[thread overview]
Message-ID: <96eef806-72df-71bc-8abb-70c26e947b3d@gmail.com> (raw)
In-Reply-To: <CAPDyKFrW7DHzc32BYE5ZiPdOdMWqGo1ch4CZZHaM1jVNjpvpWw@mail.gmail.com>

On 4/27/22 14:39, Ulf Hansson wrote:
> On Wed, 27 Apr 2022 at 20:09, Kamal Dasu <kdasu.kdev@gmail.com> wrote:
>>
>> From: Al Cooper <alcooperx@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

WARNING: multiple messages have this Message-ID (diff)
From: Florian Fainelli <f.fainelli@gmail.com>
To: Ulf Hansson <ulf.hansson@linaro.org>, Kamal Dasu <kdasu.kdev@gmail.com>
Cc: robh+dt@kernel.org, krzk+dt@kernel.org, alcooperx@gmail.com,
	bcm-kernel-feedback-list@broadcom.com, adrian.hunter@intel.com,
	linux-mmc@vger.kernel.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 2/4] mmc: sdhci-brcmstb: Enable Clock Gating to save power
Date: Wed, 27 Apr 2022 14:43:46 -0700	[thread overview]
Message-ID: <96eef806-72df-71bc-8abb-70c26e947b3d@gmail.com> (raw)
In-Reply-To: <CAPDyKFrW7DHzc32BYE5ZiPdOdMWqGo1ch4CZZHaM1jVNjpvpWw@mail.gmail.com>

On 4/27/22 14:39, Ulf Hansson wrote:
> On Wed, 27 Apr 2022 at 20:09, Kamal Dasu <kdasu.kdev@gmail.com> wrote:
>>
>> From: Al Cooper <alcooperx@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

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linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2022-04-27 21:43 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-27 18:08 [PATCH v2 0/4] mmc: sdhci-brcmstb: host controller clock enhancements Kamal Dasu
2022-04-27 18:08 ` Kamal Dasu
2022-04-27 18:08 ` [PATCH v2 1/4] mmc: sdhci-brcmstb: Re-organize flags Kamal Dasu
2022-04-27 18:08   ` Kamal Dasu
2022-05-04 10:37   ` Ulf Hansson
2022-05-04 10:37     ` Ulf Hansson
2022-04-27 18:08 ` [PATCH v2 2/4] mmc: sdhci-brcmstb: Enable Clock Gating to save power Kamal Dasu
2022-04-27 18:08   ` Kamal Dasu
2022-04-27 21:39   ` Ulf Hansson
2022-04-27 21:39     ` Ulf Hansson
2022-04-27 21:43     ` Florian Fainelli [this message]
2022-04-27 21:43       ` Florian Fainelli
2022-05-04 10:37   ` Ulf Hansson
2022-05-04 10:37     ` Ulf Hansson
2022-04-27 18:08 ` [PATCH v2 3/4] dt-bindings: mmc: Add Broadcom optional sdio_freq clock Kamal Dasu
2022-04-27 18:08   ` Kamal Dasu
2022-04-28  8:12   ` Krzysztof Kozlowski
2022-04-28  8:12     ` Krzysztof Kozlowski
2022-04-28  8:14   ` Krzysztof Kozlowski
2022-04-28  8:14     ` Krzysztof Kozlowski
2022-04-27 18:08 ` [PATCH v2 4/4] mmc: sdhci-brcmstb: Add ability to increase max clock rate for 72116b0 Kamal Dasu
2022-04-27 18:08   ` Kamal Dasu
2022-04-27 21:49   ` Florian Fainelli
2022-04-27 21:49     ` Florian Fainelli

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