linux-kernel - Re: [PATCH] spi: xilinx: Use standard num-cs binding

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Message-ID: <20150331054714.GA2869@sirena.org.uk>
Date:	Tue, 31 Mar 2015 06:47:14 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Michal Simek <michal.simek@...inx.com>
Cc:	linux-kernel@...r.kernel.org, monstr@...str.eu,
	Sören Brinkmann <soren.brinkmann@...inx.com>,
	linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] spi: xilinx: Use standard num-cs binding

On Mon, Mar 30, 2015 at 08:46:10AM +0200, Michal Simek wrote:
> On 03/27/2015 06:53 PM, Mark Brown wrote:
> > On Fri, Mar 27, 2015 at 11:55:49AM +0100, Michal Simek wrote:

> > Please fix your mail client to word wrap within paragraphs at less than
> > 80 columns - this makes your mails easier to read and reply to.

> You are the first one who had problem with this. But I have setup lower
> limit and hopefully it is better now.

That looks better, yes...  I may just be the first one who's bothered
remarking on this.

> >> On 03/08/2015 08:00 PM, Mark Brown wrote:
> >>> On Fri, Jan 16, 2015 at 01:55:14PM +0100, Michal Simek wrote:

> > Remember that we can at least in theory have additional chip selects
> > that aren't controlled by the IP block but are instead GPIOs.  

> I agree with you but this can be generic case for every SPI driver. Also
> using external decoder is possible for every driver. Maybe there are
> others options via I2C too.

Remember that this in the context of me saying I don't think num-cs is
a particularly good idea at all...

> > There's
> > also some potential confusion for users between the number of chip
> > selects in use in a given system and the size of the bitfield that the
> > driver needs to take care of.

> num-ss-bits is autogenerated directly from design tools for particular
> hardware design and this size is exactly setup and hardcoded. (num-cs
> can be just the same case)
> If there are 5 bits there are 5 wires from IP. And value of num-ss-bits
> and num-cs will be the same.

But what your patch did was *replace* num-ss-bits in the binding, not
just add it.

> If user wants to use less lines then physically available we could
> potentially extend binding to say. num-ss-bit - number of chip selects
> available in hardware. num-cs - number of chip selects used by the driver.
> But I expect that this will be rejected because it is software setting
> not hardware description.

num-cs *is* a software setting.

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