[RFC PATCH 09/12] mmc: sdhci: Use software timer when timeout greater than hardware capablility

[Kishon Vijay Abraham I]

Errata i834 in AM572x Sitara Processors Silicon Revision 2.0, 1.1
(SPRZ429K July 2014–Revised March 2017 [1]) mentions
Under high speed HS200 and SDR104 modes, the functional clock for MMC
modules will reach up to 192 MHz. At this frequency, the maximum obtainable
timeout (DTO = 0xE) through MMC host controller is (1/192MHz)*2^27 = 700ms.
Commands taking longer than 700ms may be affected by this small window
frame. Workaround for this errata is use a software timer instead of
hardware timer to provide the delay requested by the upper layer.

While this errata is specific to AM572x, it is applicable to all sdhci
based controllers when a particular request require timeout greater
than hardware capability.

Re-use the software timer already implemented in sdhci to program the
correct timeout value and also disable the hardware timeout when
the required timeout is greater than hardware capabiltiy in order to
avoid spurious timeout interrupts.

This patch is based on the earlier patch implemented for omap_hsmmc [2]

[1] -> http://www.ti.com/lit/er/sprz429k/sprz429k.pdf
[2] -> https://patchwork.kernel.org/patch/9791449/

Signed-off-by: Kishon Vijay Abraham I <kishon at ti.com>
---
 drivers/mmc/host/sdhci.c | 41 +++++++++++++++++++++++++++++++++++++++--
 drivers/mmc/host/sdhci.h | 11 +++++++++++
 2 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index e9290a3439d5..d0655e1d2cc7 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -673,6 +673,27 @@ static void sdhci_adma_table_post(struct sdhci_host *host,
 	}
 }
 
+static void sdhci_calc_sw_timeout(struct sdhci_host *host,
+				  struct mmc_command *cmd,
+				  unsigned int target_timeout)
+{
+	struct mmc_host *mmc = host->mmc;
+	struct mmc_ios *ios = &mmc->ios;
+	struct mmc_data *data = cmd->data;
+	unsigned long long transfer_time;
+
+	if (data) {
+		transfer_time = MMC_BLOCK_TRANSFER_TIME_MS(data->blksz,
+							   ios->bus_width,
+							   ios->clock);
+		/* calculate timeout for the entire data */
+		host->data_timeout = (data->blocks * (target_timeout +
+						      transfer_time));
+	} else if (cmd->flags & MMC_RSP_BUSY) {
+		host->data_timeout = cmd->busy_timeout * MSEC_PER_SEC;
+	}
+}
+
 static u8 sdhci_calc_timeout(struct sdhci_host *host, struct mmc_command *cmd)
 {
 	u8 count;
@@ -732,8 +753,12 @@ static u8 sdhci_calc_timeout(struct sdhci_host *host, struct mmc_command *cmd)
 	}
 
 	if (count >= 0xF) {
-		DBG("Too large timeout 0x%x requested for CMD%d!\n",
-		    count, cmd->opcode);
+		DBG("Too large timeout.. using SW timeout for CMD%d!\n",
+		    cmd->opcode);
+		sdhci_calc_sw_timeout(host, cmd, target_timeout);
+		host->ier &= ~SDHCI_INT_DATA_TIMEOUT;
+		sdhci_writel(host, host->ier, SDHCI_INT_ENABLE);
+		sdhci_writel(host, host->ier, SDHCI_SIGNAL_ENABLE);
 		count = 0xE;
 	}
 
@@ -1198,6 +1223,14 @@ static void sdhci_finish_command(struct sdhci_host *host)
 {
 	struct mmc_command *cmd = host->cmd;
 
+	if (host->data_timeout) {
+		unsigned long timeout;
+
+		timeout = jiffies +
+			  msecs_to_jiffies(host->data_timeout);
+		sdhci_mod_timer(host, host->cmd->mrq, timeout);
+	}
+
 	host->cmd = NULL;
 
 	if (cmd->flags & MMC_RSP_PRESENT) {
@@ -2341,6 +2374,10 @@ static bool sdhci_request_done(struct sdhci_host *host)
 		return true;
 	}
 
+	host->data_timeout = 0;
+	host->ier |= SDHCI_INT_DATA_TIMEOUT;
+	sdhci_writel(host, host->ier, SDHCI_INT_ENABLE);
+	sdhci_writel(host, host->ier, SDHCI_SIGNAL_ENABLE);
 	sdhci_del_timer(host, mrq);
 
 	/*
diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
index 54bc444c317f..e6e0278bea1a 100644
--- a/drivers/mmc/host/sdhci.h
+++ b/drivers/mmc/host/sdhci.h
@@ -332,6 +332,15 @@ struct sdhci_adma2_64_desc {
 /* Allow for a a command request and a data request at the same time */
 #define SDHCI_MAX_MRQS		2
 
+/*
+ * Time taken for transferring one block. It is multiplied by a constant
+ * factor '2' to account for any errors
+ */
+#define MMC_BLOCK_TRANSFER_TIME_MS(blksz, bus_width, freq)		\
+				   ((unsigned long long)		\
+				   (2 * (((blksz) * MSEC_PER_SEC *	\
+				   (8 / (bus_width))) / (freq))))
+
 enum sdhci_cookie {
 	COOKIE_UNMAPPED,
 	COOKIE_PRE_MAPPED,	/* mapped by sdhci_pre_req() */
@@ -546,6 +555,8 @@ struct sdhci_host {
 	/* Host SDMA buffer boundary. */
 	u32			sdma_boundary;
 
+	unsigned long long	data_timeout;
+
 	unsigned long private[0] ____cacheline_aligned;
 };
 
-- 
2.11.0