linux-kernel - [PATCH 1/2] spi: spidev: introduce SPI_IOC_WR_DEFAULT_MAX_SPEED

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Date:   Mon, 15 May 2017 10:17:11 +0200
From:   Seraphime Kirkovski <kirkseraph@...il.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org
Subject: [PATCH 1/2] spi: spidev: introduce SPI_IOC_WR_DEFAULT_MAX_SPEED_HZ
 command

christophe.blaess@...il.com, fred@...pie.com
Bcc: Subject: Re: [PATCH 1/2] spi: spidev: introduce
 SPI_IOC_WR_DEFAULT_MAX_SPEED_HZ command
Reply-To: 
In-Reply-To: <20170514092716.kqx634djffgj32r6@...ena.org.uk>

On Sun, May 14, 2017 at 06:27:16PM +0900, Mark Brown wrote:
> On Tue, May 09, 2017 at 02:24:00PM +0200, Seraphime Kirkovski wrote:
> 
> > I think, this change is necessary, on the one hand, because there are still
> > a lot of longterm[2] supported kernels out there, whose users may be relying on
> > SPI_IOC_WR_MAX_SPEED being system-wide and, on the other hand, this
> > same command has been exhibiting a different behaviour for 3 years now,
> > so its users may break, if 9169051617df7 is reverted in one way or
> > another.
> 
> Do we have any evidence that such users exist?  

I can't guarantee for other such users, but this change did disturb our 
workflow. We were using this feature to prototype and test 
hardware/firmware at different speeds.

I was thinking this morning that maybe a sysfs interface will be better 
for setting global settings. Do you prefer ?