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

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Message-ID: <YrRXTrYN3BuShbzg@sirena.org.uk>
Date:   Thu, 23 Jun 2022 13:06:38 +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 Thu, Jun 23, 2022 at 11:39:19AM +0000, Mahapatra, Amit Kumar wrote:

> > >  	/* Mode (clock phase/polarity/etc.) */
> > >  	if (of_property_read_bool(nc, "spi-cpha"))

> > This is changing the DT binding but doesn't have any updates to the binding
> > document.  The binding code also doesn't validate that we don't have too
> > many chip selects.

> The following updates are done in the binding documents for adding multiple
> CS support:
> In jedec,spi-nor.yaml file " maxItems " of the "reg" DT property has been 
> updated to accommodate two CS per SPI device.  

This is a change to a binding for a specific driver, this is changing
the SPI core.

> > I'm also not seeing anything here that checks that the driver supports
> > multiple chip selects - it seems like something that's going to cause issues
> > and we should probably have something to handle that situation.

> In my approach the chip select member (chip_select) of the spi_device structure 
> is changed to an array (chip_select[2]). This array is used to store the CS values 
> coming from the "reg" DT property. 
> In case of multiple chip selects  spi->chip_slect[0] will hold CS0 value & 
> spi->chip_select[1] wil hold CS1 value.
> In case of single chip select the spi->chip_select[0] will hold the chip select value.

That doesn't address the issue, the issue is checking that the driver
can support multiple chip selects.

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