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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Message-ID: <987cb93359dc95ce9fb387b755fadb0ab6eb98f9.camel@gmail.com>
Date:   Tue, 28 Sep 2021 11:39:59 +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 23:33 +0200, Bean Huo wrote:
> On Fri, 2021-09-24 at 16:26 +0300, Adrian Hunter wrote:
> > 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.
> 
> Adrian,
> 
> We cannot add this quirk to every host driver. This is the difference
> on the device side. In addition, I don't know what the maximum
> hardware
> timer budget for each host is. Even if you use the same SOC, the
> maximum time budget on different platforms may be different.
> 
> Assume that the maximum timeout time supported by the hardware timer
> is
> 100 milliseconds, but the maximum data transmission time required by
> the device is 150 milliseconds. In most cases, data transfer will not
> take so long. 150 is the maximum time under extreme conditions. This
> means that the device just needs to complete a data transfer within
> > 100ms and keep the data line busy. If we still use the HW timer, it
> will trigger a DATA LINE timeout interrupt.
> 
> This patch does not affect scenarios where the hardware timer meets
> the
> max data transmission time requirements of the device. It will still
> use the hardware timer. Only when the device changes, will it switch
> to
> using the SW timer.
> 
> Bean
> 

Hi Adrian,

Would you please review this patch again and is it possible to be
accepted?

Bean