linux-kernel - Re: [PATCH v2 6/6] mtd: spi-nor: core: avoid odd length/address writes in 8D-8D-8D mode

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Message-ID: <mafs0a54tsmjo.fsf@kernel.org>
Date: Thu, 24 Jul 2025 16:14:51 +0200
From: Pratyush Yadav <pratyush@...nel.org>
To: Luke Wang <ziniu.wang_1@....com>
Cc: Bough Chen <haibo.chen@....com>,  Pratyush Yadav <pratyush@...nel.org>,
  Miquel Raynal <miquel.raynal@...tlin.com>,  Tudor Ambarus
 <tudor.ambarus@...aro.org>,  "broonie@...nel.org" <broonie@...nel.org>,
  "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
  "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
  "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
  "michael@...le.cc" <michael@...le.cc>,  "p.yadav@...com"
 <p.yadav@...com>,  "richard@....at" <richard@....at>,  "vigneshr@...com"
 <vigneshr@...com>,  Han Xu <han.xu@....com>
Subject: Re: [PATCH v2 6/6] mtd: spi-nor: core: avoid odd length/address
 writes in 8D-8D-8D mode

On Tue, Jul 01 2025, Luke Wang wrote:

>> > On Mon, May 12 2025, Miquel Raynal wrote:
>> >
>> > > Hello,
>> > >
>> > > On 07/05/2025 at 09:43:25 GMT, Pratyush Yadav <pratyush@...nel.org>
[...]
>> > >
>> > > The fact is that we will have octal DTR support in SPI NAND as well at
>> > > some point, hence a common solution would be welcome as we will likely
>> > > face similar problems when performing these unaligned accesses. I
>> > > don't know how feasible it is yet, but if we have a fix for SPI NOR,
>> > > we will need something similar for SPI NAND.
[...]
>
> Sorry for delayed response.
>
> After reviewing the SPI NAND driver, I noticed that the addr and len
> alignment has already been implemented in spinand_read_from_cache_op()
> and spinand_write_to_cache_op() functions.

Right. I took a very quick look as well and it seems that SPI NAND only
does page sized reads and writes in spinand_write_to_cache_op() and
spinand_read_from_cache_op(). So it should not be a problem.

Miquel, Luke sent a respin [0] for fixing this in SPI NOR and I need to
decide if I should take them or push for a more generic fix. Did I miss
some place where SPI NAND can do odd-length reads or writes? If not, I'd
rather just take the respinned patches.

>
> Additionally, using 0xff padding in spi_mem_dirmap_write() might not
> be suitable for non-flash memory devices.

NAND also seems to be using 0xff though. From spinand_write_to_cache_op():

	nbytes = nanddev_page_size(nand) + nanddev_per_page_oobsize(nand);
	memset(spinand->databuf, 0xff, nanddev_page_size(nand));

Anyway, if needed we can solve that with a field in struct
spi_mem_dirmap_info I guess.

[0] https://lore.kernel.org/linux-mtd/20250708091646.292-1-ziniu.wang_1@nxp.com/T/#u

-- 
Regards,
Pratyush Yadav