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[PATCH 1/2] spi: spidev: introduce SPI_IOC_WR_DEFAULT_MAX_SPEED_HZ command

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  [PATCH 1/2] spi: spidev: introduce SPI_IOC_WR_DEFAULT_MAX_SPEED_HZ  command Seraphime Kirkovski <kirkseraph@gmail.com> - 2017-05-15 10:30 +0200
    Re: [PATCH 1/2] spi: spidev: introduce  SPI_IOC_WR_DEFAULT_MAX_SPEED_HZ command Mark Brown <broonie@kernel.org> - 2017-05-17 11:10 +0200

#1641374 — [PATCH 1/2] spi: spidev: introduce SPI_IOC_WR_DEFAULT_MAX_SPEED_HZ command

christophe.blaess@gmail.com, fred@haapie.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@sirena.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 ?

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#1643155 — Re: [PATCH 1/2] spi: spidev: introduce SPI_IOC_WR_DEFAULT_MAX_SPEED_HZ command

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On Mon, May 15, 2017 at 10:17:11AM +0200, Seraphime Kirkovski wrote:
> On Sun, May 14, 2017 at 06:27:16PM +0900, Mark Brown wrote:

> > 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 ?

I just don't see this as something that should be being varied at
runtime; it is supposed to be the maximum speed that the bus can be run
at, that's not something that should vary at runtime.  Possibly a sysfs
thing but honestly if you're prototyping via spidev I'd just set the
speed in your application each time it starts.

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