sata_sil24: fix sg table sizing

sil24 unnecessarily used LIBATA_MAX_PRD and ATAPI sg table was short
by one entry which might cause very obscure problems.  This patch
updates sg table sizing such that

* One full page is used for PRB + sg table.  On 4k page,
  this results in 253 sg's.

* Make ATAPI sg block properly sized.

* Make build fail if command block size doesn't equal PAGE_SIZE.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

1 files changed, 23 insertions, 3 deletions

diff --git a/drivers/ata/sata_sil24.c b/drivers/ata/sata_sil24.c
index 187dcb02c681..96fd5260446d 100644
--- a/drivers/ata/sata_sil24.c
+++ b/drivers/ata/sata_sil24.c
@@ -63,6 +63,21 @@ enum {
         SIL24_HOST_BAR          = 0,
         SIL24_PORT_BAR          = 2,
 
+        /* sil24 fetches in chunks of 64bytes.  The first block
+         * contains the PRB and two SGEs.  From the second block, it's
+         * consisted of four SGEs and called SGT.  Calculate the
+         * number of SGTs that fit into one page.
+         */
+        SIL24_PRB_SZ            = sizeof(struct sil24_prb)
+                                  + 2 * sizeof(struct sil24_sge),
+        SIL24_MAX_SGT           = (PAGE_SIZE - SIL24_PRB_SZ)
+                                  / (4 * sizeof(struct sil24_sge)),
+
+        /* This will give us one unused SGEs for ATA.  This extra SGE
+         * will be used to store CDB for ATAPI devices.
+         */
+        SIL24_MAX_SGE           = 4 * SIL24_MAX_SGT + 1,
+
         /*
          * Global controller registers (128 bytes @ BAR0)
          */
@@ -247,13 +262,13 @@ enum {
 
 struct sil24_ata_block {
         struct sil24_prb prb;
-        struct sil24_sge sge[LIBATA_MAX_PRD];
+        struct sil24_sge sge[SIL24_MAX_SGE];
 };
 
 struct sil24_atapi_block {
         struct sil24_prb prb;
         u8 cdb[16];
-        struct sil24_sge sge[LIBATA_MAX_PRD - 1];
+        struct sil24_sge sge[SIL24_MAX_SGE];
 };
 
 union sil24_cmd_block {
@@ -378,7 +393,7 @@ static struct scsi_host_template sil24_sht = {
         .change_queue_depth     = ata_scsi_change_queue_depth,
         .can_queue              = SIL24_MAX_CMDS,
         .this_id                = ATA_SHT_THIS_ID,
-        .sg_tablesize           = LIBATA_MAX_PRD,
+        .sg_tablesize           = SIL24_MAX_SGE,
         .cmd_per_lun            = ATA_SHT_CMD_PER_LUN,
         .emulated               = ATA_SHT_EMULATED,
         .use_clustering         = ATA_SHT_USE_CLUSTERING,
@@ -1284,6 +1299,7 @@ static void sil24_init_controller(struct ata_host *host)
 
 static int sil24_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 {
+        extern int __MARKER__sil24_cmd_block_is_sized_wrongly;
         static int printed_version;
         struct ata_port_info pi = sil24_port_info[ent->driver_data];
         const struct ata_port_info *ppi[] = { &pi, NULL };
@@ -1292,6 +1308,10 @@ static int sil24_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
         int i, rc;
         u32 tmp;
 
+        /* cause link error if sil24_cmd_block is sized wrongly */
+        if (sizeof(union sil24_cmd_block) != PAGE_SIZE)
+                __MARKER__sil24_cmd_block_is_sized_wrongly = 1;
+
         if (!printed_version++)
                 dev_printk(KERN_DEBUG, &pdev->dev, "version " DRV_VERSION "\n");