openwrt/target/linux/brcm2708/patches-4.4/0185-bcm2835-sdhost-Workaround-for-slow-sectors.patch

From a4a7cdd3364de9fa9edfb32a64fa0e7a577d9143 Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.org>
Date: Tue, 15 Mar 2016 14:10:29 +0000
Subject: [PATCH] bcm2835-sdhost: Workaround for "slow" sectors

Some cards have been seen to cause timeouts after certain sectors are
read. This workaround enforces a minimum delay between the stop after
reading one of those sectors and a subsequent data command.

Using CMD23 (SET_BLOCK_COUNT) avoids this problem, so good cards will
not be penalised by this workaround.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
---
 drivers/mmc/host/bcm2835-sdhost.c | 50 +++++++++++++++++++++++++++++++++++----
 1 file changed, 46 insertions(+), 4 deletions(-)

--- a/drivers/mmc/host/bcm2835-sdhost.c
+++ b/drivers/mmc/host/bcm2835-sdhost.c
@@ -202,9 +202,12 @@ struct bcm2835_host {
 	int				max_delay;	/* maximum length of time spent waiting */
 	struct timeval			stop_time;	/* when the last stop was issued */
 	u32				delay_after_stop; /* minimum time between stop and subsequent data transfer */
+	u32				delay_after_this_stop; /* minimum time between this stop and subsequent data transfer */
 	u32				overclock_50;	/* frequency to use when 50MHz is requested (in MHz) */
 	u32				overclock;	/* Current frequency if overclocked, else zero */
 	u32				pio_limit;	/* Maximum block count for PIO (0 = always DMA) */
+
+	u32				sectors;	/* Cached card size in sectors */
 };
 
 #if ENABLE_LOG
@@ -425,6 +428,7 @@ static void bcm2835_sdhost_reset_interna
 	bcm2835_sdhost_set_power(host, true);
 	mdelay(10);
 	host->clock = 0;
+	host->sectors = 0;
 	bcm2835_sdhost_write(host, host->hcfg, SDHCFG);
 	bcm2835_sdhost_write(host, host->cdiv, SDCDIV);
 	mmiowb();
@@ -880,6 +884,24 @@ static void bcm2835_sdhost_prepare_data(
 	host->flush_fifo = 0;
 	host->data->bytes_xfered = 0;
 
+	if (!host->sectors && host->mmc->card) {
+		struct mmc_card *card = host->mmc->card;
+		if (!mmc_card_sd(card) && mmc_card_blockaddr(card)) {
+			/*
+			 * The EXT_CSD sector count is in number of 512 byte
+			 * sectors.
+			 */
+			host->sectors = card->ext_csd.sectors;
+		} else {
+			/*
+			 * The CSD capacity field is in units of read_blkbits.
+			 * set_capacity takes units of 512 bytes.
+			 */
+			host->sectors = card->csd.capacity <<
+				(card->csd.read_blkbits - 9);
+		}
+	}
+
 	if (!host->dma_desc) {
 		/* Use PIO */
 		int flags = SG_MITER_ATOMIC;
@@ -989,7 +1011,7 @@ bool bcm2835_sdhost_send_command(struct
 
 	if (cmd->data) {
 		log_event("CMDD", cmd->data->blocks, cmd->data->blksz);
-		if (host->delay_after_stop) {
+		if (host->delay_after_this_stop) {
 			struct timeval now;
 			int time_since_stop;
 			do_gettimeofday(&now);
@@ -998,12 +1020,32 @@ bool bcm2835_sdhost_send_command(struct
 				/* Possibly less than one second */
 				time_since_stop = time_since_stop * 1000000 +
 					(now.tv_usec - host->stop_time.tv_usec);
-				if (time_since_stop < host->delay_after_stop)
-					udelay(host->delay_after_stop -
+				if (time_since_stop <
+				    host->delay_after_this_stop)
+					udelay(host->delay_after_this_stop -
 					       time_since_stop);
 			}
 		}
 
+		host->delay_after_this_stop = host->delay_after_stop;
+		if ((cmd->data->flags & MMC_DATA_READ) && !host->use_sbc) {
+			/* See if read crosses one of the hazardous sectors */
+			u32 first_blk, last_blk;
+
+			/* Intentionally include the following sector because
+			   without CMD23/SBC the read may run on. */
+			first_blk = host->mrq->cmd->arg;
+			last_blk = first_blk + cmd->data->blocks;
+
+			if (((last_blk >= (host->sectors - 64)) &&
+			     (first_blk <= (host->sectors - 64))) ||
+			    ((last_blk >= (host->sectors - 32)) &&
+			     (first_blk <= (host->sectors - 32)))) {
+				host->delay_after_this_stop =
+					max(250u, host->delay_after_stop);
+			}
+		}
+
 		if (cmd->data->flags & MMC_DATA_WRITE)
 			sdcmd |= SDCMD_WRITE_CMD;
 		if (cmd->data->flags & MMC_DATA_READ)
@@ -1078,7 +1120,7 @@ static void bcm2835_sdhost_transfer_comp
 			if (!host->use_busy)
 				bcm2835_sdhost_finish_command(host, NULL);
 
-			if (host->delay_after_stop)
+			if (host->delay_after_this_stop)
 				do_gettimeofday(&host->stop_time);
 		}
 	} else {