On 03/11/20 05:05PM, Vignesh Raghavendra wrote: > > > On 11/1/20 3:14 AM, Richard Weinberger wrote: > > On Tue, Oct 27, 2020 at 12:24 PM Pratyush Yadav <[email protected]> wrote: > >>> [0] > >>> https://lore.kernel.org/linux-mtd/[email protected]/ > >> > >> Ping. Any comments on the series? > > > > From the UBIFS point of view I'd like to avoid as many device specific > > settings as possible. > > We check already for NOR flash, checking for NOR *and* > > SPI_NOR_NO_MULTI_PASS_PP > > feels a bit clumsy. > > > > Tudor, what do you think about SPI_NOR_NO_MULTI_PASS_PP? > > This kind of NOR seems to be a little NAND'ish. Maybe we can hide this > > detail > > in the mtd framework? > > > > Agree with Richard. I don't see need for SPI_NOR_NO_MULTI_PASS_PP. From > MTD point of view setting mtd->writesize to be equal to pagesize should > be enough. Its upto clients of MTD devices to ensure there is no multi > pass programming within a "writesize" block.
That is what I initially thought too but then I realized that multi-pass programming is completely different from page-size programming. Instead of writing 4 bytes twice, you can zero out the entire page in one single operation. You would be compliant with the write size requirement but you still do multi-pass programming because you did not erase the page before this operation. It is also not completely correct to say the Cypress S28 flash has a write size of 256. You _can_ write one byte if you want. You just can't write to that page again without erasing it first. For example, if a file system only wants to write 128 bytes on a page, it can do so without having to write the whole page. It just needs to make sure it doesn't write to it again without erasing first. nor_erase_prepare() was written to handle quirks of some specific devices. Not every device starts filling zeroes from the end of a page. So we have device-specific code in UBIFS already. You will obviously need device-specific settings to have control over that code. One might argue that we should move nor_erase_prepare() out of UBIFS. But requiring a flash to start erasing from the start of the page is a UBIFS-specific requirement. Other users of a flash might not care about it at all. And so we have ourselves a bit of a conundrum. Adding SPI_NOR_NO_MULTI_PASS_PP is IMHO the least disruptive answer. If the file system wants to do multi-pass page programming on NOR flashes, how else do we tell it not to do it for this specific flash? > If this is not clear in the current documentation of struct mtd, then > that can be updated. -- Regards, Pratyush Yadav Texas Instruments India
