linux-kernel - Re: [PATCH 3/3] spi: s3c64xx: support interrupt based pio mode

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Date:   Tue, 4 Apr 2023 22:15:05 +0900
From:   Jaewon Kim <jaewon02.kim@...sung.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Andi Shyti <andi@...zian.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Rob Herring <robh+dt@...nel.org>, linux-spi@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Chanho Park <chanho61.park@...sung.com>
Subject: Re: [PATCH 3/3] spi: s3c64xx: support interrupt based pio mode

Hello Mark,


On 23. 4. 4. 21:58, Mark Brown wrote:
> On Tue, Apr 04, 2023 at 03:00:11PM +0900, Jaewon Kim wrote:
>
>> This patch adds IRQ based PIO mode instead of cpu polling.
>> By using the FIFO trigger level, interrupts are received.
>> CPU consumption is reduced in PIO mode because registers are not
>> constantly checked.
> Is there some lower limit where it's still worth using polling, for
> example for just one or two bytes like a register address?  Taking an
> interrupt isn't free...


I did not considers lower limit.
According to your review, interrupt seems to be called too often.
However, It can't prevent the CPU utilization going to 100% during spi 
transmission.
We will give more consideration and deliver a better solution to the 
next patch version.


Thanks

Jaewon Kim