linux-kernel - Re: [PATCH v4 05/16] mtd: spi-nor: default to address width of 3 for configurable widths

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Date:   Tue, 28 Apr 2020 09:34:46 +0800
From:   Yicong Yang <yangyicong@...ilicon.com>
To:     Pratyush Yadav <me@...avpratyush.com>
CC:     Pratyush Yadav <p.yadav@...com>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Mark Brown <broonie@...nel.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <linux-spi@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Sekhar Nori <nsekhar@...com>
Subject: Re: [PATCH v4 05/16] mtd: spi-nor: default to address width of 3 for
 configurable widths

Hi Pratyush,


On 2020/4/28 1:23, Pratyush Yadav wrote:
> Hi Yicong,
>
> On 26/04/20 11:53AM, Yicong Yang wrote:
>> On 2020/4/25 2:43, Pratyush Yadav wrote:
>>> JESD216D.01 says that when the address width can be 3 or 4, it defaults
>>> to 3 and enters 4-byte mode when given the appropriate command. So, when
>>> we see a configurable width, default to 3 and let flash that default to
>>> 4 change it in a post-bfpt fixup.
>>>
>>> This fixes SMPT parsing for flashes with configurable address width. If
>>> the SMPT descriptor advertises variable address width, we use
>>> nor->addr_width as the address width. But since it was not set to any
>>> value from the SFDP table, the read command uses an address width of 0,
>>> resulting in an incorrect read being issued.
>>>
>>> Signed-off-by: Pratyush Yadav <p.yadav@...com>
>>> ---
>>>  drivers/mtd/spi-nor/sfdp.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/drivers/mtd/spi-nor/sfdp.c b/drivers/mtd/spi-nor/sfdp.c
>>> index f917631c8110..5cecc4ba2141 100644
>>> --- a/drivers/mtd/spi-nor/sfdp.c
>>> +++ b/drivers/mtd/spi-nor/sfdp.c
>>> @@ -460,6 +460,7 @@ static int spi_nor_parse_bfpt(struct spi_nor *nor,
>>>  	/* Number of address bytes. */
>>>  	switch (bfpt.dwords[BFPT_DWORD(1)] & BFPT_DWORD1_ADDRESS_BYTES_MASK) {
>>>  	case BFPT_DWORD1_ADDRESS_BYTES_3_ONLY:
>>> +	case BFPT_DWORD1_ADDRESS_BYTES_3_OR_4:
>>>  		nor->addr_width = 3;
>>>  		break;
>> Should we also assign address width to 3 in default condition. At least we should not
>> leave it uninitialized here.
> The default condition would be taken when this field is 3. The value 3 
> is reserved, and so no current device should use this value. That said, 
> I don't see any downsides of doing so. If the value 3 means something 
> else in later revisions of the standard, this code would need to change 
> anyway. If not, we would use a relatively sane default for devices with 
> a faulty BFPT.

The purpose is to set one possible value which may be used later in parsing smpt.
In current driver, if we do nothing with the post-bfpt fixup, then the width will
be unset. Otherwise, maybe the width can also be set in spi_nor_smpt_addr_width()

    default:
   +    if (!nor->addr_width)
   +        nor->addr_width = 3;
        return nor->addr_width;

But set when parsing bfpt seems more reasonable.

> I haven't received any comments on my series so far. If end up having to
> re-roll it, I will add this change. Otherwise, I'm not sure if it is a 
> good idea to re-roll a 16-patch series for a one liner that isn't fixing 
> some major bug. In that case, maybe you can send an independent patch 
> that does this after mine is merged?

Fine. :)

Regards,
Yicong