linux-kernel - Re: [PATCH] mmc: sdhci-msm: pervent access to suspended controller

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Date: Thu, 4 Apr 2024 23:13:02 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Adrian Hunter <adrian.hunter@...el.com>
Cc: Mantas Pucka <mantas@...vices.com>, Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konrad.dybcio@...aro.org>, Georgi Djakov <djakov@...nel.org>, 
	Pramod Gurav <pramod.gurav@...aro.org>, Ritesh Harjani <ritesh.list@...il.com>, 
	linux-mmc@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
	Thierry Reding <thierry.reding@...il.com>, Liming Sun <limings@...dia.com>, 
	Victor Shih <victor.shih@...esyslogic.com.tw>
Subject: Re: [PATCH] mmc: sdhci-msm: pervent access to suspended controller

On Thu, 4 Apr 2024 at 20:42, Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> On 28/03/24 16:20, Adrian Hunter wrote:
> > On 27/03/24 17:17, Ulf Hansson wrote:
> >> On Tue, 26 Mar 2024 at 11:25, Adrian Hunter <adrian.hunter@...el.com> wrote:
> >>>
> >>> On 21/03/24 16:30, Mantas Pucka wrote:
> >>>> Generic sdhci code registers LED device and uses host->runtime_suspended
> >>>> flag to protect access to it. The sdhci-msm driver doesn't set this flag,
> >>>> which causes a crash when LED is accessed while controller is runtime
> >>>> suspended. Fix this by setting the flag correctly.
> >>>>
> >>>> Cc: stable@...r.kernel.org
> >>>> Fixes: 67e6db113c90 ("mmc: sdhci-msm: Add pm_runtime and system PM support")
> >>>> Signed-off-by: Mantas Pucka <mantas@...vices.com>
> >>>
> >>> Acked-by: Adrian Hunter <adrian.hunter@...el.com>
> >>
> >> Looks like this problem may exist for other sdhci drivers too. In
> >> particular for those that enables runtime PM, don't set
> >> SDHCI_QUIRK_NO_LED and don't use sdhci_runtime|suspend_resume_host().
> >>
> >> Don't know if there is a better way to address this, if not on a case
> >> by case basis. Do you have any thoughts about this?
> >
> > Yes probably case by case, but I will look at it.
>
> There seem to be 3 that use runtime pm but not
> sdhci_runtime_suspend_host():
>
> 1. dwcmshc_runtime_suspend() : only turns off the card clock
> via SDHCI_CLOCK_CONTROL register, so registers are presumably
> still accessible
>
> 2. gl9763e_runtime_suspend() : ditto
>
> 3. sdhci_tegra_runtime_suspend() : disables the functional
> clock via clk_disable_unprepare(), so registers are presumably
> still accessible
>
> sdhci_msm_runtime_suspend() is different because it also turns
> off the interface clock.
>
> But it looks like there are no similar cases.

Not sure we should care, but it still looks a bit fragile to me. We
may also have a power-domain hooked up to the device, that could get
power gated too, in which case it's likely affecting the access to
registers.

Kind regards
Uffe