linux-kernel - Re: [RFC PATCH 1/2] spi: Add multiple CS support for a single SPI device

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Date:   Tue, 19 Jul 2022 18:53:25 +0100
From:   Mark Brown <broonie@...nel.org>
To:     "Mahapatra, Amit Kumar" <amit.kumar-mahapatra@....com>
Cc:     Amit Kumar Mahapatra <amit.kumar-mahapatra@...inx.com>,
        "p.yadav@...com" <p.yadav@...com>,
        "miquel.raynal@...tlin.com" <miquel.raynal@...tlin.com>,
        "richard@....at" <richard@....at>,
        "vigneshr@...com" <vigneshr@...com>,
        "git@...inx.com" <git@...inx.com>,
        "michal.simek@...inx.com" <michal.simek@...inx.com>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "michael@...le.cc" <michael@...le.cc>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "git (AMD-Xilinx)" <git@....com>
Subject: Re: [RFC PATCH 1/2] spi: Add multiple CS support for a single SPI
 device

On Tue, Jul 19, 2022 at 01:21:41PM +0000, Mahapatra, Amit Kumar wrote:

> I agree, so for checking the controller multiple chip select capability(using 
> more than one chip select at once) we can define a new spi controller DT 
> property like "multi-cs-cap"(please suggest a better name). 
> The controller that can support multiple chip selects should have this property 
> in the spi controller DT node. The spi core will check ctlr->multi-cs-cap to 
> operate multiple chip select in parallel.

I'm not sure this needs to be a DT property, it's more just something we
infer from the compatible.  The name seems fine, as does the flag in the
controller data.

> > the chip selects are available and that the controller can do something useful
> > with them (and probably have an implementation in the core for doing so via
> > GPIO).

> Here are you referring to the usecase in which a controller implementing multi CS
> support using GPIO?  

Yes, we probably ought to.

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