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sd: Clear PS bit before Mode Select. 

According to SPC-4, in a Mode Select, the PS bit in Mode Pages is
reserved and must be set to 0 by the driver.  In the sd implementation,
function cache_type_store does a Mode Sense, which might set the PS bit
on the read buffer, followed by a Mode Select, which receives the same
buffer, without explicitly clearing the PS bit.  So, in cases where
target supports saving the Mode Page to a non-volatile location, we end
up doing a Mode Select with the PS bit set, which could cause an illegal
request error if the target is checking this.

This was observed on a new firmware change, which was subsequently
reverted, but this changes sd.c to be more compliant with SPC-4.

This patch clears the PS bit in the buffer returned by Mode Select,
right before it is used in the Mode Select command.

Signed-off-by: Gabriel Krisman Bertazi <krisman@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Gabriel Krisman Bertazi 2015-10-30 16:04:43 -02:00 committed by Martin K. Petersen
parent 3467a1468f
commit 2c5d16d6a9
1 changed files with 1 additions and 0 deletions
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1
drivers/scsi/sd.c
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@ -204,6 +204,7 @@ cache_type_store(struct device *dev, struct device_attribute *attr,
buffer_data[2] &= ~0x05;
buffer_data[2] |= wce << 2 | rcd;
sp = buffer_data[0] & 0x80 ? 1 : 0;
buffer_data[0] &= ~0x80;
if (scsi_mode_select(sdp, 1, sp, 8, buffer_data, len, SD_TIMEOUT,
SD_MAX_RETRIES, &data, &sshdr)) {