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
b...@biot.com
