linux-kernel - Re: [PATCH 0/5] spi: zynqmp-gqspi: Improve error recovery by resetting

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Message-ID: <39ad89bf-880e-4ae9-bbdb-4d388dd14a7d@linux.dev>
Date: Tue, 21 Jan 2025 11:51:18 -0500
From: Sean Anderson <sean.anderson@...ux.dev>
To: Mark Brown <broonie@...nel.org>
Cc: Miquel Raynal <miquel.raynal@...tlin.com>,
 Michal Simek <michal.simek@....com>, linux-spi@...r.kernel.org,
 linux-kernel@...r.kernel.org, Jinjie Ruan <ruanjinjie@...wei.com>,
 linux-arm-kernel@...ts.infradead.org,
 Amit Kumar Mahapatra <amit.kumar-mahapatra@....com>,
 Conor Dooley <conor+dt@...nel.org>, Krzysztof Kozlowski
 <krzk+dt@...nel.org>, Rob Herring <robh@...nel.org>,
 devicetree@...r.kernel.org
Subject: Re: [PATCH 0/5] spi: zynqmp-gqspi: Improve error recovery by
 resetting

On 1/20/25 08:49, Mark Brown wrote:
> On Fri, Jan 17, 2025 at 04:46:23PM -0500, Sean Anderson wrote:
>> On 1/17/25 13:41, Mark Brown wrote:
>> > On Fri, Jan 17, 2025 at 07:31:08PM +0100, Miquel Raynal wrote:
> 
>> >> Yes, unless the timeout is reached for "good reasons", ie. you request
>> >> substantial amounts of data (typically from a memory device) and the
>> >> timeout is too short compared to the theoretical time spent in the
>> >> transfer. A loaded machine can also increase the number of false
>> >> positives I guess.
> 
>> > I'd argue that all of those are bad reasons, I'd only expect us to time
>> > out when there's a bug - choosing too low a timeout or doing things in a
>> > way that generates timeouts under load is a problem.
> 
>> There's no transmit DMA for this device. So if you are under high load
>> and make a long transfer, it's possible to time out. I don't know if
>> it's possible to fix that very easily. The timeout calculation assumes
>> that data is being transferred at the SPI bus rate.
> 
> In that case I wouldn't expect the timeout to apply to the whole
> operation, or I'd expect a timeout applied waiting for something
> interrupt driven to not to be fired unless we stop making forward
> progress.  

I don't know if there are any helpers we can use for this. To implement
this we'd need something like schedule_timeout() but where the interrupt
handler calls mod_timer() whenever it does work.

--Sean