linux-kernel - Re: [PATCH V3] spi: spi-geni-qcom: Add SPI driver support for GENI based QUP

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Date:   Mon, 10 Sep 2018 09:27:09 +0530
From:   dkota@...eaurora.org
To:     Doug Anderson <dianders@...omium.org>
Cc:     Stephen Boyd <swboyd@...omium.org>,
        Mark Brown <broonie@...nel.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-soc@...r.kernel.org>,
        devicetree@...r.kernel.org,
        Girish Mahadevan <girishm@...eaurora.org>
Subject: Re: [PATCH V3] spi: spi-geni-qcom: Add SPI driver support for GENI
 based QUP


>> I see there is no need of taking the spinlock as timeout will be 
>> handled
>> after the calculated time as per data size and speed.
>> There is 99.9% less chances of interrupt during the timeout handler.
>>> 
>>> 
>>> 
>>> https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/1201081
> 
> The thing is, we want it to be 100% reliable, not 99.9% reliable.  Is
> it somehow wrong to add the spinlock?  ...or are you noticing
> performance problems with the spinlock there?  It's just nice not to
> have to think about it.

As I said, timeout will be handled after the calculated time as per data 
size and speed. Enough time is given for interrupt, there is no chance 
of interrupt occurrence during the handle_fifo_timeout(). So there is no 
need of spinlock.