Re: [PATCH v10 1/6] dt-bindings: mmc: Extend keep-power-in-suspend beyond SDIO

[Shawn Lin <shawn.lin@linux.dev>]

在 2026/10/28 星期三 3:46, Ulf Hansson 写道:
> On Tue, Oct 27, 2026 at 4:02 PM Shawn Lin <shawn.lin@linux.dev> wrote:
>>
>> Hi
>>
>> 在 2026/10/27 星期二 22:40, Ulf Hansson 写道:
>>> From: Kamal Dasu <kamal.dasu@broadcom.com>
>>>
>>> keep-power-in-suspend is currently documented as SDIO-only, but the
>>> requirement it describes -- preserving card power across a
>>> suspend/resume cycle -- applies just as well to any card type. Drop
>>> the SDIO-only restriction so eMMC and SD platforms can use it too.
>>>
>>
>> I don't see how SD could use it from the following patches. Perhaps we
>> should still be more strict here to say SDIO and eMMC only, unless
>> SD part is implemented later.
> 
> I didn't have the bandwidth to implement this for SD at this very
> moment, but the idea is to add it for SD too.
> 

SDIO devices have a clear wake-on-host requirement, so keeping power on
is reasonable. eMMC and SD are passively accessed devices, making this a
pseudo-requirement under system freeze conditions until Broadcom chips
changed the situation for eMMC.

However, for the SD part, I doubt such a need exists. It would require
dedicated ROM code support, and unlike eMMC, SD is not used as primary
storage. Worse still, unlike eMMC and SDIO devices which are soldered
down, vendors typically have an AVL to certify board-mounted components,
while SD cards can be freely swapped. The compatibility of off-the-shelf
SD cards is relatively poor, so I question whether there is a real-world
scenario for SD cards here. If there is no such scenario, this is dead
code.

> That said, I was also thinking that maybe it would make sense to add a
> sysfs node to allow the behavior to be controlled by userspace.
> Thoughts?
> 

Sure, regarding the sysfs node you mentioned, we already have
mmc_caps2_set() exposed to userspace, and we can add
MMC_CAP2_RESET_AT_RESUME support there

>>
>>> Signed-off-by: Kamal Dasu <kamal.dasu@broadcom.com>
>>> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
>>> ---
>>>    .../devicetree/bindings/mmc/mmc-controller-common.yaml          | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml b/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
>>> index 8b9b3b036129..2fc8e06d5ec9 100644
>>> --- a/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
>>> +++ b/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
>>> @@ -301,7 +301,7 @@ properties:
>>>      keep-power-in-suspend:
>>>        $ref: /schemas/types.yaml#/definitions/flag
>>>        description:
>>> -      SDIO only. Preserves card power during a suspend/resume cycle.
>>> +      Preserves card power during a suspend/resume cycle.
>>>
>>>      wakeup-source:
>>>        $ref: /schemas/types.yaml#/definitions/flag
>>
> 
> Kind regards
> Uffe