mmc: omap: fix broken PIO mode

After commit 26b8852 ("mmc: omap_hsmmc: remove private DMA API implementation"), the Nokia N800 here stopped booting: [ 2.086181] Waiting for root device /dev/mmcblk0p1... [ 2.324066] Unhandled fault: imprecise external abort (0x406) at 0x00000000 [ 2.331451] Internal error: : 406 [#1] ARM [ 2.335784] Modules linked in: [ 2.339050] CPU: 0 Not tainted (3.6.0-rc3 torvalds#60) [ 2.344146] PC is at default_idle+0x28/0x30 [ 2.348602] LR is at trace_hardirqs_on_caller+0x15c/0x1b0 ... This turned out to be due to memory corruption caused by long-broken PIO code in drivers/mmc/host/omap.c. (Previously, this driver had been using DMA; but the above commit caused the MMC driver to fall back to PIO mode with an unmodified Kconfig.) The PIO code, added with the rest of the driver in commit 730c9b7 ("[MMC] Add OMAP MMC host driver"), confused bytes with 16-bit words. This bug caused memory located after the PIO transfer buffer to be corrupted with transfers larger than 32 bytes. The driver also did not increment the buffer pointer after the transfer occurred. This bug resulted in data corruption during any transfer larger than 64 bytes. Signed-off-by: Paul Walmsley <paul@pwsan.com> Reviewed-by: Felipe Balbi <balbi@ti.com> Tested-by: Tony Lindgren <tony@atomide.com> Signed-off-by: Chris Ball <cjb@laptop.org>

Author: Paul Walmsley

drivers/mmc/host/omap.c

@@ -668,7 +668,7 @@ mmc_omap_clk_timer(unsigned long data)
 static void
 mmc_omap_xfer_data(struct mmc_omap_host *host, int write)
 {
-int n;
+int n, nwords;
 
 if (host->buffer_bytes_left == 0) {
 host->sg_idx++;
@@ -678,15 +678,23 @@ mmc_omap_xfer_data(struct mmc_omap_host *host, int write)
 n = 64;
 if (n > host->buffer_bytes_left)
 n = host->buffer_bytes_left;
+
+nwords = n / 2;
+nwords += n & 1; /* handle odd number of bytes to transfer */
+
 host->buffer_bytes_left -= n;
 host->total_bytes_left -= n;
 host->data->bytes_xfered += n;
 
 if (write) {
-__raw_writesw(host->virt_base + OMAP_MMC_REG(host, DATA), host->buffer, n);
+__raw_writesw(host->virt_base + OMAP_MMC_REG(host, DATA),
+ host->buffer, nwords);
 } else {
-__raw_readsw(host->virt_base + OMAP_MMC_REG(host, DATA), host->buffer, n);
+__raw_readsw(host->virt_base + OMAP_MMC_REG(host, DATA),
+ host->buffer, nwords);
 }
+
+host->buffer += nwords;
 }
 
 static inline void mmc_omap_report_irq(u16 status)