linux-kernel - Re: [PATCH 3/3] doc: dt: mtd: stop referring to driver code for spi-nor IDs

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Date:	Tue, 17 Nov 2015 11:04:55 -0300
From:	Javier Martinez Canillas <javier@....samsung.com>
To:	Brian Norris <computersforpeace@...il.com>,
	linux-mtd@...ts.infradead.org
Cc:	linux-kernel@...r.kernel.org,
	Rafał Miłecki <zajec5@...il.com>,
	devicetree@...r.kernel.org
Subject: Re: [PATCH 3/3] doc: dt: mtd: stop referring to driver code for
 spi-nor IDs

Hello Brian,

On 11/16/2015 07:34 PM, Brian Norris wrote:
> Pull the supported chip names from drivers/mtd/devices/m25p80.c and stop
> pointing readers to Linux code.
> 
> Also (although I see this habit repeated throughout the
> Documentation/devicetree/bindings/ tree), stop using the title "driver"

Agreed.

> in this file, when we're trying explicitly to describe hardware, not
> software.
> 
> Signed-off-by: Brian Norris <computersforpeace@...il.com>
> Cc: <devicetree@...r.kernel.org>
> ---
>  .../devicetree/bindings/mtd/jedec,spi-nor.txt      | 56 ++++++++++++++++++++--
>  1 file changed, 51 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt
> index 2bee68103b01..2c91c03e7eb0 100644
> --- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt
> +++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt
> @@ -1,15 +1,61 @@
> -* MTD SPI driver for ST M25Pxx (and similar) serial flash chips
> +* SPI NOR flash: ST M25Pxx (and similar) serial flash chips
>  
>  Required properties:
>  - #address-cells, #size-cells : Must be present if the device has sub-nodes
>    representing partitions.
>  - compatible : May include a device-specific string consisting of the
> -               manufacturer and name of the chip. Bear in mind the DT binding
> -               is not Linux-only, but in case of Linux, see the "m25p_ids"
> -               table in drivers/mtd/devices/m25p80.c for the list of supported
> -               chips.
> +               manufacturer and name of the chip. A list of supported chip
> +               names follows.

Here says that the compatible string consists of manufacturer and name...

>                 Must also include "jedec,spi-nor" for any SPI NOR flash that can
>                 be identified by the JEDEC READ ID opcode (0x9F).
> +
> +               Supported chip names:
> +                 at25df321a
> +                 at25df641
> +                 at26df081a
> +                 mr25h256
> +                 mx25l4005a
> +                 mx25l1606e
> +                 mx25l6405d
> +                 mx25l12805d
> +                 mx25l25635e
> +                 n25q064
> +                 n25q128a11
> +                 n25q128a13
> +                 n25q512a
> +                 s25fl256s1
> +                 s25fl512s
> +                 s25sl12801
> +                 s25fl008k
> +                 s25fl064k
> +                 sst25vf040b
> +                 m25p40
> +                 m25p80
> +                 m25p16
> +                 m25p32
> +                 m25p64
> +                 m25p128
> +                 w25x80
> +                 w25x32
> +                 w25q32
> +                 w25q32dw
> +                 w25q80bl
> +                 w25q128
> +                 w25q256
> +

... but the entries in the list don't have a manufacturer. I know this is
due backward compatibility because as we discussed in the thread mentioned
in the cover letter, the SPI core didn't use the manufacturer and that
implementation detail leaked into the DTBs.

But I think that either only the correct list with vendor should be added
to the DT binding docs (but make sure that backward compatibility in the
driver and SPI core is maintained) or both the wrong and correct list should
be documented and the former be marked as deprecated.

> +               The following chip names have been used historically to
> +               designate quirky versions of flash chips that do not support the
> +               JEDEC READ ID opcode (0x9F):
> +                 m25p05-nonjedec
> +                 m25p10-nonjedec
> +                 m25p20-nonjedec
> +                 m25p40-nonjedec
> +                 m25p80-nonjedec
> +                 m25p16-nonjedec
> +                 m25p32-nonjedec
> +                 m25p64-nonjedec
> +                 m25p128-nonjedec
> +

Same here, I would prefer if the DT binding make it clear that not having
a vendor is wrong and is only documented to maintain backward compatibility.

>  - reg : Chip-Select number
>  - spi-max-frequency : Maximum frequency of the SPI bus the chip can operate at
>  
> 

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America
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