RE: [RFC PATCH 1/2] spi: Add multiple CS support for a single SPI device

From: "Mahapatra, Amit Kumar" <amit.kumar-mahapatra@amd.com>
To: Mark Brown <broonie@kernel.org>, Michal Simek <michal.simek@xilinx.com>
Cc: Amit Kumar Mahapatra <amit.kumar-mahapatra@xilinx.com>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	"p.yadav@ti.com" <p.yadav@ti.com>,
	"miquel.raynal@bootlin.com" <miquel.raynal@bootlin.com>,
	"richard@nod.at" <richard@nod.at>,
	"vigneshr@ti.com" <vigneshr@ti.com>,
	"git@xilinx.com" <git@xilinx.com>,
	"linux-spi@vger.kernel.org" <linux-spi@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"michael@walle.cc" <michael@walle.cc>,
	"linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>,
	"git (AMD-Xilinx)" <git@amd.com>,
	"Mahapatra, Amit Kumar" <amit.kumar-mahapatra@amd.com>
Subject: RE: [RFC PATCH 1/2] spi: Add multiple CS support for a single SPI device
Date: Fri, 15 Jul 2022 15:36:23 +0000	[thread overview]
Message-ID: <DM6PR12MB2809BA6D4F94EA59E76E6576DC8B9@DM6PR12MB2809.namprd12.prod.outlook.com> (raw)
In-Reply-To: <Ysw5MpvjKM5LKvWd@sirena.org.uk>

Hello Mark,

> -----Original Message-----
> From: Mark Brown <broonie@kernel.org>
> Sent: Monday, July 11, 2022 8:23 PM
> To: Michal Simek <michal.simek@xilinx.com>
> Cc: Amit Kumar Mahapatra <amit.kumar-mahapatra@xilinx.com>; Krzysztof
> Kozlowski <krzysztof.kozlowski+dt@linaro.org>; p.yadav@ti.com;
> miquel.raynal@bootlin.com; richard@nod.at; vigneshr@ti.com;
> git@xilinx.com; linux-spi@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org; michael@walle.cc;
> linux-mtd@lists.infradead.org
> Subject: Re: [RFC PATCH 1/2] spi: Add multiple CS support for a single SPI
> device
> 
> On Mon, Jul 11, 2022 at 02:47:54PM +0200, Michal Simek wrote:
> > On 6/9/22 13:54, Mark Brown wrote:
> > > On Mon, Jun 06, 2022 at 04:56:06PM +0530, Amit Kumar Mahapatra
> wrote:
> 
> > > > +	u32 cs[SPI_CS_CNT_MAX];
> > > > +	u8 idx;
> > > >   	/* 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.
> 
> > I would like to better understand your request here in connection to
> > change in the binding code for validation.
> > What exactly do you want to validate?
> > That child reg property is not bigger than num-cs in controller node?
> 
> If you are adding support for multiple chip selects in the driver then there
> must be some mechanism for expressing that in the bindings which I would
> expect to see appear as a change to the binding document.

Thank you for the clarification.
As per my understanding we would not be needing a new DT 
property for expressing multi chip select support in the driver.
We can use "num-cs" property of the spi controller for 
broadcasting multi chip select support of the driver.
If "num-cs" value is greater than 1 then the driver can support 
multiple chip selects.

Please let us know if you have any other approach in mind.

Regards,
Amit

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