linux-kernel - Re: [PATCH v1 2/2] mmc: sdhci: Use the SW timer when the HW timer cannot meet the timeout value required by the device

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Date:   Fri, 24 Sep 2021 16:26:37 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Bean Huo <huobean@...il.com>, Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Bean Huo <beanhuo@...ron.com>, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] mmc: sdhci: Use the SW timer when the HW timer
 cannot meet the timeout value required by the device

On 24/09/21 4:08 pm, Bean Huo wrote:
> On Fri, 2021-09-24 at 15:17 +0300, Adrian Hunter wrote:
>>>>>          sdhci_writeb(host, count, SDHCI_TIMEOUT_CONTROL);
>>>>> }
>>>>> The driver has detected that the hardware timer cannot meet the
>>>>> timeout
>>>>> requirements of the device, but we still use the hardware
>>>>> timer,
>>>>> which will
>>>>> allow potential timeout issuea . Rather than allowing a
>>>>> potential
>>>>> problem to exist, why can’t software timing be used to avoid
>>>>> this
>>>>> problem?
>>>> Timeouts aren't that accurate.  The maximum is assumed still to
>>>> work.
>>>> mmc->max_busy_timeout is used to tell the core what the maximum
>>>> is.
>>> mmc->max_busy_timeout is still a representation of Host HW timer
>>> maximum timeout count, isn't it? 
>>
>>
>> Not necessarily.  For SDHCI_QUIRK2_DISABLE_HW_TIMEOUT it would be
>>
>> set to zero to indicate no maximum.
> 
> yes, this is the purpose of the patch, for the host controller without
> quirk SDHCI_QUIRK2_DISABLE_HW_TIMEOUT, if the timeout count required by
> device is beyond the HW timer max count, we choose SW timer to avoid the HW timer timeout IRQ.
> 
> I don't know if I get it correctly.

Why can't drivers that want the behaviour just set the quirk?

Drivers that do not work with the quirk, do not have to set it.