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 15:08:08 +0200
From:   Bean Huo <huobean@...il.com>
To:     Adrian Hunter <adrian.hunter@...el.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 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.

Bean