On Wed, Feb 24 2010, Ramya Desai wrote: > On Tue, Feb 23, 2010 at 11:31 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > Dear Alan, > > Thanks a lot. > > > So Ramya, it looks like you need to edit store_max_sectors() in > > drivers/usb/storage/scsiglue.c. Get rid of the " && ms <= > > SCSI_DEFAULT_MAX_SECTORS" part. > > > > Then you should be able to write a large value to > > /sys/block/sdX/device/max_sectors to increase the hardware limit. The > > new value divided by 2 will show up in > > /sys/block/sdX/queue/max_hw_sectors_kb. > > > > Once that limit is increased, you can write a large value to > > /sys/block/sdX/queue/max_sectors_kb. That should give you long > > transfer lengths. > > I did exactly. I removed the following statement from > store_max_sectors (drivers/usb/storage/scsiglue.c) function. > " && ms <= SCSI_DEFAULT_MAX_SECTORS". I also changed the .max_sectors > = 2048 in the host template. > > Then I restarted the system and build the usb-storage without any issue. > > After inserting my device, I found 1024 in > /sys/block/sdb/device/max_sectors. So, I tried to increase the value > through echo 2048 > /sys/block/sdb/device/max_sectors. When I do this, > it invoked the store_max_sectors() in the scsiglue.c file and able to > see ms (the variable in the store_max_sectors()) is 2048. But, the > value in the /sys/block/sdb/device/max_sectors is still 1024 only. > > When I looked into the /sys/block/sdb/queue/max_hw_sectors_kb, it > shows 1024, which is 2048 sectors. Then, I tried to increase the value > in /sys/block/sdb/queue/max_sectors_kb through echo 1024 > > /sys/block/sdb/queue/max_sectors_kb. After this, I saw 1024 in the > /sys/block/sdb/queue/max_sectors_kb. When I see 1024 in > /sys/block/sdb/queue/max_sectors_kb then I found 2048 in > /sys/block/sdb/device/max_sectors. However, this time, still my device > received 512 KB (1024) data transfer buffers in scsi_command. > > Please let me know If I missed any thing here? You cannot make max_sectors_kb larger than max_hw_sectors_kb, as the latter implies a hardware restriction (as seen by the block layer). Drivers should not fiddle with max_sectors_kb, they should only concern themselves with max_hw_sectors. The former is then set to a reasonable value, which is either the system default or the hardware limit, which ever one is lower. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
