On Tue, Aug 23, 2016 at 5:37 AM, Tom Yan [off-list ref] wrote:

On 22 August 2016 at 04:23, Shaun Tancheff [off-list ref] wrote:

quoted

+/**
+ * ata_format_dsm_trim_descr() - SATL Write Same to ATA SCT Write Same
+ * @cmd: SCSI command being translated
+ * @lba: Starting sector
+ * @num: Number of logical sectors to be zero'd.
+ *
+ * Rewrite the WRITE SAME descriptor to be an SCT Write Same formatted
+ * descriptor.
+ * NOTE: Writes a pattern (0's) in the foreground.
+ *       Large write-same requents can timeout.
+ */
+static void ata_format_sct_write_same(struct scsi_cmnd *cmd, u64 lba, u64 num)
+{
+       u16 *sctpg;
+       unsigned long flags;
+
+       spin_lock_irqsave(&ata_scsi_rbuf_lock, flags);
+       sctpg = ((void *)ata_scsi_rbuf);

Because ata_scsi_rbuf is of a fixed size of ATA_SCSI_RBUF_SIZE.

#define ATA_SCSI_RBUF_SIZE      4096
...
static u8 ata_scsi_rbuf[ATA_SCSI_RBUF_SIZE];

quoted

+
+       put_unaligned_le16(0x0002,  &sctpg[0]); /* SCT_ACT_WRITE_SAME */
+       put_unaligned_le16(0x0101,  &sctpg[1]); /* WRITE PTRN FG */
+       put_unaligned_le64(lba,     &sctpg[2]);
+       put_unaligned_le64(num,     &sctpg[6]);
+       put_unaligned_le32(0u,      &sctpg[10]);
+
+       sg_copy_from_buffer(scsi_sglist(cmd), scsi_sg_count(cmd), sctpg, 512);

You have no reason to use 512 here instead of ATA_SCSI_RBUF_SIZE this time.

Ah .. because SCT Write Same is a fixed 512 byte transfer?
Ah .. because I only have 512 bytes to copy?

quoted

+       spin_unlock_irqrestore(&ata_scsi_rbuf_lock, flags);
+}