[ARM] 3751/1: i.MX/MX1 SD/MMC use 512 bytes request for SCR read

Patch from Pavel Pisa

This is another approach to SDHC deficiency workaround.
It seems, that previous solution based on 16 bytes (FIFO length size)
read is still timing sensitive on genirq and fully preemptive kernels.
The new solution is backuped by M9328 UM statement, that only 512 byte
block are working properly and by 2.4.26 FreeScale's SDHC code.

Jay Monkman reports significant improvement on code based
on this driver after applying this change on MX21 as well.
Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

drivers/mmc/imxmmc.c

@@ -91,6 +91,8 @@ struct imxmci_host {
 	int			dma_allocated;
 
 	unsigned char		actual_bus_width;
+
+	int			prev_cmd_code;
 };
 
 #define IMXMCI_PEND_IRQ_b	0
@@ -248,16 +250,14 @@ static void imxmci_setup_data(struct imxmci_host *host, struct mmc_data *data)
 	 * partial FIFO fills and reads. The length has to be rounded up to burst size multiple.
 	 * This is required for SCR read at least.
 	 */
-	if (datasz < 64) {
+	if (datasz < 512) {
 		host->dma_size = datasz;
 		if (data->flags & MMC_DATA_READ) {
 			host->dma_dir = DMA_FROM_DEVICE;
 
 			/* Hack to enable read SCR */
-			if(datasz < 16) {
 			MMC_NOB = 1;
-				MMC_BLK_LEN = 16;
-			}
+			MMC_BLK_LEN = 512;
 		} else {
 			host->dma_dir = DMA_TO_DEVICE;
 		}
@@ -409,6 +409,9 @@ static void imxmci_finish_request(struct imxmci_host *host, struct mmc_request *
 
 	spin_unlock_irqrestore(&host->lock, flags);
 
+	if(req && req->cmd)
+		host->prev_cmd_code = req->cmd->opcode;
+
 	host->req = NULL;
 	host->cmd = NULL;
 	host->data = NULL;
@@ -553,7 +556,6 @@ static int imxmci_cpu_driven_data(struct imxmci_host *host, unsigned int *pstat)
 {
 	int i;
 	int burst_len;
-	int flush_len;
 	int trans_done = 0;
 	unsigned int stat = *pstat;
 
@@ -566,44 +568,43 @@ static int imxmci_cpu_driven_data(struct imxmci_host *host, unsigned int *pstat)
 	dev_dbg(mmc_dev(host->mmc), "imxmci_cpu_driven_data running STATUS = 0x%x\n",
 		stat);
 
+	udelay(20);	/* required for clocks < 8MHz*/
+
 	if(host->dma_dir == DMA_FROM_DEVICE) {
 		imxmci_busy_wait_for_status(host, &stat,
 				STATUS_APPL_BUFF_FF | STATUS_DATA_TRANS_DONE,
-				20, "imxmci_cpu_driven_data read");
+				50, "imxmci_cpu_driven_data read");
 
 		while((stat & (STATUS_APPL_BUFF_FF |  STATUS_DATA_TRANS_DONE)) &&
-		      (host->data_cnt < host->dma_size)) {
-			if(burst_len >= host->dma_size - host->data_cnt) {
-				flush_len = burst_len;
-				burst_len = host->dma_size - host->data_cnt;
-				flush_len -= burst_len;
-				host->data_cnt = host->dma_size;
-				trans_done = 1;
-			} else {
-				flush_len = 0;
-				host->data_cnt += burst_len;
-			}
+		      (host->data_cnt < 512)) {
 
-			for(i = burst_len; i>=2 ; i-=2) {
-				*(host->data_ptr++) = MMC_BUFFER_ACCESS;
 			udelay(20);	/* required for clocks < 8MHz*/
-			}
 
-			if(i == 1)
-				*(u8*)(host->data_ptr) = MMC_BUFFER_ACCESS;
+			for(i = burst_len; i>=2 ; i-=2) {
+				u16 data;
+				data = MMC_BUFFER_ACCESS;
+				udelay(10);	/* required for clocks < 8MHz*/
+				if(host->data_cnt+2 <= host->dma_size) {
+					*(host->data_ptr++) = data;
+				} else {
+					if(host->data_cnt < host->dma_size)
+						*(u8*)(host->data_ptr) = data;
+				}
+				host->data_cnt += 2;
+			}
 
 			stat = MMC_STATUS;
 
-			/* Flush extra bytes from FIFO */
-			while(flush_len && !(stat & STATUS_DATA_TRANS_DONE)){
-				i = MMC_BUFFER_ACCESS;
-				stat = MMC_STATUS;
-				stat &= ~STATUS_CRC_READ_ERR; /* Stupid but required there */
+			dev_dbg(mmc_dev(host->mmc), "imxmci_cpu_driven_data read %d burst %d STATUS = 0x%x\n",
+				host->data_cnt, burst_len, stat);
 		}
 
-			dev_dbg(mmc_dev(host->mmc), "imxmci_cpu_driven_data read burst %d STATUS = 0x%x\n",
-				burst_len, stat);
-		}
+		if((stat & STATUS_DATA_TRANS_DONE) && (host->data_cnt >= 512))
+			trans_done = 1;
+
+		if(host->dma_size & 0x1ff)
+			stat &= ~STATUS_CRC_READ_ERR;
+
 	} else {
 		imxmci_busy_wait_for_status(host, &stat,
 				STATUS_APPL_BUFF_FE,
@@ -692,8 +693,8 @@ static void imxmci_tasklet_fnc(unsigned long data)
 		       what, stat, MMC_INT_MASK);
 		dev_err(mmc_dev(host->mmc), "CMD_DAT_CONT = 0x%04x, MMC_BLK_LEN = 0x%04x, MMC_NOB = 0x%04x, DMA_CCR = 0x%08x\n",
 		       MMC_CMD_DAT_CONT, MMC_BLK_LEN, MMC_NOB, CCR(host->dma));
-		dev_err(mmc_dev(host->mmc), "CMD%d, bus %d-bit, dma_size = 0x%x\n",
-		       host->cmd?host->cmd->opcode:0, 1<<host->actual_bus_width, host->dma_size);
+		dev_err(mmc_dev(host->mmc), "CMD%d, prevCMD%d, bus %d-bit, dma_size = 0x%x\n",
+		       host->cmd?host->cmd->opcode:0, host->prev_cmd_code, 1<<host->actual_bus_width, host->dma_size);
 	}
 
 	if(!host->present || timeout)