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>
Cc: Amit Kumar Mahapatra <amit.kumar-mahapatra@xilinx.com>,
	"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>,
	"michal.simek@xilinx.com" <michal.simek@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>
Subject: RE: [RFC PATCH 1/2] spi: Add multiple CS support for a single SPI device
Date: Wed, 27 Jul 2022 13:02:31 +0000	[thread overview]
Message-ID: <BN7PR12MB2802E2A9079E505932832270DC979@BN7PR12MB2802.namprd12.prod.outlook.com> (raw)
In-Reply-To: <YtbvlYZoRDz6i+pS@sirena.org.uk>

Hello Mark,

> -----Original Message-----
> From: Mark Brown <broonie@kernel.org>
> Sent: Tuesday, July 19, 2022 11:23 PM
> To: Mahapatra, Amit Kumar <amit.kumar-mahapatra@amd.com>
> Cc: Amit Kumar Mahapatra <amit.kumar-mahapatra@xilinx.com>;
> p.yadav@ti.com; miquel.raynal@bootlin.com; richard@nod.at;
> vigneshr@ti.com; git@xilinx.com; michal.simek@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;
> git (AMD-Xilinx) <git@amd.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.

I agree that we can infer this from the compatible and set 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.

In my next version I will add the implementation in the spi core for multi CS support using GPIO, but I will not be able test it as I don't have the necessary hardware setup .

Regards,
Amit  