Messages in this thread | | | Date | Sat, 19 Apr 2008 09:51:36 +0200 | From | Pierre Ossman <> | Subject | [RFC] MMC multiwrite capability removal |
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Hi everyone,
I've been planning to remove the MMC multiwrite capability (making it always on), but I need some help from all you driver maintainers first.
Ages ago, I had a chat with Axboe about the current situation and it turns out that the MMC layer is a bit over-cautious. There are plenty of other block devices that cannot report anything more than success/failure for the whole request. So it's silly that we're crippling the MMC layer when upper layers have to deal with that scenario anyway.
What I need from you is and audit of your respective driver(s) and check that they do not overestimate the number of successfully written blocks. Please send a short reply even if your driver needs no changes.
Long version:
The data flow of a write is something like this:
1. Data starts moving from main memory to host memory (DMA or PIO) 2. Data finishes moving from main memory to host memory 3. A sector moves to the front of the device write queue 4. The sector starts being sent over the wire 5. The sector finishes being sent over the wire 6. The card acknowledges a successful transfer 7. The card finishes busy signalling 8. The sector moves to the front of the card write queue 9. The sector gets picked up by the FTL 10. The sector is written to media
In a perfect world we would report the number of sectors that made it to 10. Unfortunately we have limited insight into what the card is up to.
What your host drivers should report is sectors that have passed stage 6. If your controller doesn't give you enough information to determine that, then you must report 0 for all failed transfers.
I'll be having a closer look at stages 7 through 10, but that's a core issue that shouldn't involve your drivers.
Rgds
-- -- Pierre Ossman
Linux kernel, MMC maintainer http://www.kernel.org PulseAudio, core developer http://pulseaudio.org rdesktop, core developer http://www.rdesktop.org
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