linux-kernel - Re: [PATCH 2/9] mtd: spi-nor: add an alternative method to support memory >16MiB

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Date:   Wed, 5 Oct 2016 14:53:07 +0200
From:   Cyrille Pitchen <cyrille.pitchen@...el.com>
To:     Vignesh R <vigneshr@...com>, <computersforpeace@...il.com>,
        <linux-mtd@...ts.infradead.org>
CC:     <marex@...x.de>, <boris.brezillon@...e-electrons.com>,
        <nicolas.ferre@...el.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/9] mtd: spi-nor: add an alternative method to support
 memory >16MiB

Hi Vignesh,

Le 05/10/2016 à 14:12, Vignesh R a écrit :
> Hi,
> 
> 
> On Tuesday 04 October 2016 10:07 PM, Cyrille Pitchen wrote:
> [...]
>>  static struct seq_rw_config stfsm_s25fl_write4_configs[] = {
>> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
>> index 5c87b2d99507..423448c1c7a8 100644
>> --- a/drivers/mtd/spi-nor/spi-nor.c
>> +++ b/drivers/mtd/spi-nor/spi-nor.c
>> @@ -75,6 +75,10 @@ struct flash_info {
>>  					 * bit. Must be used with
>>  					 * SPI_NOR_HAS_LOCK.
>>  					 */
>> +#define SPI_NOR_4B_OPCODES	BIT(10)	/*
>> +					 * Use dedicated 4byte address op codes
>> +					 * to support memory size above 128Mib.
>> +					 */
> 
> 
> I don't see this flag being added to any flash_info data for any m25p80
> compatible flashes? Is that part of a separate series?
> 

Indeed, this flag is not used yet by any entry in the spi_nor_ids[] array.
At first, I tested this patch with a Macronix mx25l25673g memory.
This memory shares the very same JEDEC ID as the older mx25l25635e, so
I added the SPI_NOR_4B_OPCODES flag in the mx25l25635e entry during my test.
However I didn't commit this change since the actual mx25l25635e memory
doesn't support The 4-byte address instruction test.

Also the mx25l25673g provides the optional 4-byte Address Instruction Table,
as described in the JESD216 rev B specification, so patches 6 and 7 allow
to use the 4-byte address op codes without setting the SPI_NOR_4B_OPCODES flag.

Hence the SPI_NOR_4B_OPCODES, will be useful for memories which don't
provide the JESD216B 4-byte Address Instruction Table but still support
the associated op code. It will have to be tested for each individual entry
in the spi_nor_ids[] array, which can be done later.

Anyway, the 4-byte address op codes introduced by this patch are also used
by patch 7 (parse SFDP 4-byte Address Instruction Table).

Best regards,

Cyrille