Hi Jaehoon, Seungwon, Ulf, On Thu, 2015-06-25 at 11:25 +-0300, Alexey Brodkin wrote: +AD4- As per DW MobileStorage databook +ACI-each descriptor can transfer up to +AD4- 4kB +AD4- of data in chained mode+ACI-, moreover buffer size that is put in +ACI-des1+ACI- +AD4- is +AD4- limited to 13 bits, i.e. for example on attempt to +AD4- IDMAC+AF8-SET+AF8-BUFFER1+AF8-SIZE(desc, 8192) size value that's effectively +AD4- written +AD4- will be 0. +AD4- +AD4- On the platform with 8kB PAGE+AF8-SIZE I see dw+AF8-mmc gets data blocks in +AD4- SG-list of 8kB size and that leads to unpredictable behavior of the +AD4- SD/MMC controller. +AD4- +AD4- In particular on write to FAT partition of SD-card the controller +AD4- will +AD4- stuck in the middle of DMA transaction. +AD4- +AD4- Solution to the problem is simple - we need to pass large (+AD4- 4kB) +AD4- data +AD4- buffers to the controller via multiple descriptors. And that's what +AD4- that change does. +AD4- +AD4- What's interesting I did try original driver on same platform but +AD4- configured with 4kB PAGE+AF8-SIZE and may confirm that data blocks passed +AD4- in SG-list to dw+AF8-mmc never exeed 4kB limit - that explains why nobody +AD4- ever faced a problem I did. +AD4- +AD4- Signed-off-by: Alexey Brodkin +ADw-abrodkin+AEA-synopsys.com+AD4- +AD4- Cc: Seungwon Jeon +ADw-tgih.jun+AEA-samsung.com+AD4- +AD4- Cc: Jaehoon Chung +ADw-jh80.chung+AEA-samsung.com+AD4- +AD4- Cc: Ulf Hansson +ADw-ulf.hansson+AEA-linaro.org+AD4- +AD4- Cc: arc-linux-dev+AEA-synopsys.com +AD4- Cc: linux-kernel+AEA-vger.kernel.org +AD4- --- +AD4- drivers/mmc/host/dw+AF8-mmc.c +AHw- 109 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+------- +AD4- ---------- I'm wondering if there're any comments on that patch or if it could be applied? It fixes a real problem on systems on 4K PAGE+AF8-SIZE so would be good to have it in upstream. In particular this is the case with ARC AXS board which made its way in upstream kernel recently. Regards, Alexey-- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
