linux-kernel - RE: [PATCH v1 1/1] mtd: devices: add ACPI support for non-jedec m25p80

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Message-ID: <f03c76b1d0cb49848371915f53f9784d@asem.it>
Date:   Thu, 7 Mar 2019 17:50:19 +0000
From:   Flavio Suligoi <f.suligoi@...m.it>
To:     David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        "Marek Vasut" <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        "Mark Brown" <broonie@...nel.org>,
        Frieder Schrempf <frieder.schrempf@...eet.de>,
        Yogesh Gaur <yogeshnarayan.gaur@....com>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v1 1/1] mtd: devices: add ACPI support for non-jedec
 m25p80

> -----Original Message-----
> From: David Woodhouse <dwmw2@...radead.org>
> Sent: giovedì 7 marzo 2019 18:40
> To: Flavio Suligoi <f.suligoi@...m.it>; Brian Norris
> <computersforpeace@...il.com>; Boris Brezillon <bbrezillon@...nel.org>;
> Marek Vasut <marek.vasut@...il.com>; Richard Weinberger <richard@....at>;
> Mark Brown <broonie@...nel.org>; Frieder Schrempf
> <frieder.schrempf@...eet.de>; Yogesh Gaur <yogeshnarayan.gaur@....com>;
> linux-mtd@...ts.infradead.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH v1 1/1] mtd: devices: add ACPI support for non-jedec
> m25p80
> 
> On Tue, 2019-02-26 at 11:48 +0100, Flavio Suligoi wrote:
> > For the x86 machines a m25p80-compatible device have to be declared
> using
> > an ACPI table (which can be directly a part of the BIOS ACPI tables).
> >
> > In this case it is necessary to add the device in the "of_device_id"
> structure
> > list, to permit the device name matching by the ACPI kernel functions.
> >
> > This is an example of a SSDT table for the Everspin mr25h40:
> >
> > DefinitionBlock ("mr25h40.aml", "SSDT", 5, "ASEMsp", "MR25H40", 1)
> > {
> > 	External (_SB.SPI1, DeviceObj)
> >
> > 	Scope (\_SB.SPI1)
> > 	{
> > 		Device (NVR0)
> > 		{
> > 			Name (_HID, "PRP0001")
> > 			Name (_DDN, "Everspin MR25H40 MRAM")
> > 			Name (_CRS, ResourceTemplate () {
> > 				SpiSerialBus (
> > 				1,                      // Chip select
> > 				PolarityLow,            // Chip select is active
> low
> > 				FourWireMode,           // Full duplex
> > 				8,                      // Bits per word is 8
> (byte)
> > 				ControllerInitiated,    // Don't care
> > 				10000000,               // 10 MHz
> > 				ClockPolarityLow,       // SPI mode 0
> ClockPolarityLow
> > 				ClockPhaseFirst,        // SPI mode 0
> ClockPhaseFirst
> > 				"\\_SB.SPI1",      	// SPI host controller
> > 				0,			// Must be 0
> > 				ResourceConsumer,
> > 				,
> > 				)
> > 			})
> >
> > 			Name (_DSD, Package () {
> > 				ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> > 				Package () {
> > 					Package () {"compatible", "mr25h40"},
> > 				}
> > 			})
> > 		}
> > 	}
> > }
> >
> > Signed-off-by: Flavio Suligoi <f.suligoi@...m.it>
> 
> Why use the specific chip name in the "compatible" property? Why isn't
> it using "jedec,spi-nor"?
> 
> Does this still actually get passed through to spi_nor_scan()... and is
> it *necessary*? Can't the chips be probed?
> 

Hi David,

exactly, the mr25h40 is not Jedec compatible, so it can't be probed, 
so it is necessary to identify it explicitly.

Flavio