linux-kernel - Re: [PATCH] mtd: spi-nor: Fix 3-or-4 address byte mode logic

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Message-ID: <73a258f3-45dd-1354-d5fd-904d5e372d2c@microchip.com>
Date:   Tue, 6 Oct 2020 11:19:14 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <p.yadav@...com>, <bert@...t.com>
CC:     <miquel.raynal@...tlin.com>, <richard@....at>, <vigneshr@...com>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mtd: spi-nor: Fix 3-or-4 address byte mode logic

On 10/6/20 2:03 PM, Tudor Ambarus - M18064 wrote:
> On 10/1/20 9:34 AM, Pratyush Yadav wrote:
>> So using an address width of 4 here is not necessarily the right thing
>> to do. This change would break SMPT parsing for all flashes that use
>> 3-byte addressing by default because SMPT parsing can involve register
>> reads/writes. One such device is the Cypress S28HS flash. In fact, this
>> was what prompted me to write the patch [0].
> 
> Do you refer to spi_nor_get_map_in_use()?

oh, I see. If addr width is set via the SMPT_CMD_ADDRESS_LEN_USE_CURRENT,
case, and if the flash comes in 4 byte address mode from a bootloader,
then setting addr_width to 3 in case BFPT_DWORD1_ADDRESS_BYTES_3_OR_4,
will break the reading of the map.

If the Address Mode bit is volatile, maybe we can reset the flash to
its power on state immediately after identification. For the NV bits,
we have the same recurring problem.