From: Bert Vermeulen <bert@biot.com>
To: Pratyush Yadav <p.yadav@ti.com>
Cc: vigneshr@ti.com, tudor.ambarus@microchip.com, richard@nod.at,
linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org,
miquel.raynal@bootlin.com
Subject: Re: [PATCH] mtd: spi-nor: Fix 3-or-4 address byte mode logic
Date: Fri, 2 Oct 2020 00:22:44 +0200 [thread overview]
Message-ID: <801445c9-4f59-5300-3a03-b48a3d631efe@biot.com> (raw)
In-Reply-To: <20201001063421.qcjdikj2tje3jn6k@ti.com>
On 10/1/20 8:34 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].
>
> Before that patch, how did MX25L25635F decide to use 4-byte addressing?
The SoCs I'm dealing with have an SPI_ADDR_SEL pin, indicating whether it
should be in 3 or 4-byte mode. The vendor's hacked-up U-Boot sets the mode
accordingly, as does their BSP. It seems to me like a misfeature, and I want
to just ignore it and do reasonable JEDEC things, but I have the problem
that the flash chip can be in 4-byte mode by the time it gets to my spi-nor
driver.
> Coming out of BFPT parsing addr_width would still be 0. My guess is that
> it would go into spi_nor_set_addr_width() with addr_width still 0 and
> then the check for (nor->mtd.size > 0x1000000) would set it to 4. Do I
> guess correctly?
No, it comes out of that with addr_width=3 because the chip publishes 3_OR_4
and hence gets 3, even if that's nonsensical for a 32MB chip to publish.
Certainly that's the problem, I just want to solve it in a more general case
than just a fixup for this chip.
> In that case maybe we can do a better job of deciding what gets priority
> in the if-else chain. For example, giving addr_width from nor->info
> precedence over the one configured by SFDP can solve this problem. Then
> all you have to do is set the addr_width in the info struct, which is
> certainly easier than adding a fixup hook. There may be a more elegant
> solution to this but I haven't given it much thought.
Since Tudor doesn't want the order of sfdp->info changed, how about
something like this instead?
+++ b/drivers/mtd/spi-nor/core.c
@@ -3028,13 +3028,15 @@ static int spi_nor_set_addr_width(struct spi_nor *nor)
/* already configured from SFDP */
} else if (nor->info->addr_width) {
nor->addr_width = nor->info->addr_width;
- } else if (nor->mtd.size > 0x1000000) {
- /* enable 4-byte addressing if the device exceeds 16MiB */
- nor->addr_width = 4;
} else {
nor->addr_width = 3;
}
+ if (nor->addr_width == 3 && nor->mtd.size > 0x1000000) {
+ /* enable 4-byte addressing if the device exceeds 16MiB */
+ nor->addr_width = 4;
+ }
+
Still fixes the general case, but I'm not sure what the SMPT parsing problem
is -- would this still trigger it?
--
Bert Vermeulen
bert@biot.com
______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/
next prev parent reply other threads:[~2020-10-01 22:24 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-30 23:56 [PATCH] mtd: spi-nor: Fix 3-or-4 address byte mode logic Bert Vermeulen
2020-10-01 6:34 ` Pratyush Yadav
2020-10-01 14:15 ` Tudor.Ambarus
2020-10-01 22:22 ` Bert Vermeulen [this message]
2020-10-02 7:50 ` David Laight
2020-10-04 21:12 ` Bert Vermeulen
2020-10-04 21:36 ` David Laight
2020-10-06 23:19 ` Joel Stanley
2020-10-06 11:03 ` Tudor.Ambarus
2020-10-06 11:19 ` Tudor.Ambarus
2020-10-06 11:40 ` Pratyush Yadav
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=801445c9-4f59-5300-3a03-b48a3d631efe@biot.com \
--to=bert@biot.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mtd@lists.infradead.org \
--cc=miquel.raynal@bootlin.com \
--cc=p.yadav@ti.com \
--cc=richard@nod.at \
--cc=tudor.ambarus@microchip.com \
--cc=vigneshr@ti.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).