linux-kernel - Re: [PATCH 4/5] spi: bcm-qspi: Make multiple data blocks interrupt-driven

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Message-ID: <20200616082648.GE4447@sirena.org.uk>
Date:   Tue, 16 Jun 2020 09:26:48 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Mark Tomlinson <Mark.Tomlinson@...iedtelesis.co.nz>
Cc:     "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "kdasu.kdev@...il.com" <kdasu.kdev@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/5] spi: bcm-qspi: Make multiple data blocks
 interrupt-driven

On Tue, Jun 16, 2020 at 03:07:17AM +0000, Mark Tomlinson wrote:
> On Mon, 2020-06-15 at 15:32 +0100, Mark Brown wrote:

> > Again was this done for a reason and if so do we understand why doing
> > this from interrupt context is safe - how long can the interrupts be
> > when stuffing the FIFO from interrupt context?

> As I'm porting a Broadcom patch, I'm hoping someone else can add
> something to this. From the history it appears there was a hard limit

If you didn't write this code then it should have at least one signoff
from the original source, I can't do anything with this without signoffs
- please see Documentation/process/submitting-patches.rst for what this
is and why it's important.

> (no small chunks), and this was changed to doing it in chunks with
> patch 345309fa7c0c92, apparently to improve performance. I believe this
> change further improves performance, but as the patch arrived without
> any documentation, I'm not certain.

Have you tested the impact on performance?

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