Messages in this thread | | | Date | Fri, 1 Apr 2016 14:05:04 +1100 | From | James Cameron <> | Subject | Re: [PATCH for-4.4 1/2] mtd: spi-nor: fix Spansion regressions (aliased with Winbond) |
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On Wed, Mar 30, 2016 at 02:47:48PM +0200, Cyrille Pitchen wrote: > Hi all, > > [...] > > But this is interesting: I see the latest datasheet for Spansion > > s25fl064k says it supports the Block Protect bits in the Status > > Register, so presumably *some* version of s25fl064k should support > > write_sr(nor, 0) to unlock it at boot... > > > > If Felix's initial report is indeed correct, then I think we have: > > (1) Spansion s25fl064k without Block Protect support (that breaks if you > > try to write SR=0) > > (2) Spansion s25fl064k with Block Protect support (that requires you to > > unlock at boot by writing SR=0 (?)) > > (3) Winbond w25q64 with Block Protect support (that requires you to > > unlock at boot by writing SR=0) > > > > And (1)-(3) all report the same ID, and (1) is incompatible with (2) and > > (3). Am I right? Are flash vendors really this insane? Should we all > > just give up and go home? > > > > Just a general remark: maybe reading the JEDEC ID is not a so reliable mean to > discover SPI flash hardware capabilities at runtime. > > Two weeks ago some Macronix people came to Atmel to present us next evolutions > of SPI flashes. We took this opportunity to ask them some questions and one of > them was about memories with different hardware capabilities sharing the very > same JEDEC ID. One example is Macronix MX25L25635E vs MX25L25673G. > > They explained to us that for Macronix memories, the 2byte product ID is to be > split into a 1byte code for the memory type and a second byte for the memory > denstity. For instance: > C2: Manufacturer ID, Macronix > 20: Memory Type, SPI NOR flash > 19: Memory density, 256Mib > > Hence the JEDEC ID only provides information about the memory size and all > SPI NOR memories of a given size actually share the same JEDEC ID.
Yes, that's true.
(Reference: Open Firmware SPI Flash driver used at OLPC.)
> > Similar cases can also be found with other manufacturers: Micron, Winbond, > Spansion... > > Also the Macronix engineers asked us how software applications drive the (Q)SPI > memories. I answered them that Linux or u-boot use a static table indexed by > the JEDEC ID, which provides the hardware capabilities. I guess they didn't > expect software developers to use the JEDEC ID for this purpose. > Well, it's just a feeling. > > Then the Macronix engineers proposed to use the Serial Flash Discoverable > Parameter (SFDP) tables to make the difference between memories sharing the > same JEDEC ID. This might help us in some cases. > However we should be cautious when using this standard: last year, I've tried > to discover hardware parameters through these tables when I was working with > Spansion and Micron memories. I found out the Parameter Table Pointers inside > the SFDP Header were expressed as byte offset with one memory and as dword > offset with the other. > So I gave up using these tables since some memories diverged from the standard, > which was "work in progress" at that time.
Yes, I too was unable to use SFDP; some devices didn't have them, some didn't seem to be good data.
> > Anyway if we cannot completely rely on the SFDP tables we could still use > DT properties but we should no longer expect to guess all hardware parameters > from the JEDEC ID alone.
We solved this problem by not using our SPI Flash from the kernel, but that's not the best outcome. ;-)
> > Best regards, > > Cyrille
-- James Cameron http://quozl.netrek.org/
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