mmc: mmci: stm32: manage block gap hardware flow control

In stm32 sdmmc variant revision v3.0, a block gap hardware flow control
should be used with bus speed modes SDR104 and HS200.
It is enabled by writing a non-null value to the new added register
MMCI_STM32_FIFOTHRR.
The threshold will be 2^(N-1) bytes, so we can use the ffs() function to
compute the value N to be written to the register. The threshold used
should be the data block size, but must not be bigger than the FIFO size.

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Link: https://lore.kernel.org/r/20230619115120.64474-5-yann.gautier@foss.st.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: Yann-lms

drivers/mmc/host/mmci.h

@@ -218,6 +218,11 @@
 #define MCI_STM32_BUSYD0ENDMASK	BIT(21)
 
 #define MMCIMASK1		0x040
+
+/* STM32 sdmmc data FIFO threshold register */
+#define MMCI_STM32_FIFOTHRR	0x044
+#define MMCI_STM32_THR_MASK	GENMASK(3, 0)
+
 #define MMCIFIFOCNT		0x048
 #define MMCIFIFO		0x080 /* to 0x0bc */
 

drivers/mmc/host/mmci_stm32_sdmmc.c

@@ -361,6 +361,19 @@ static u32 sdmmc_get_dctrl_cfg(struct mmci_host *host)
 
 	datactrl = mmci_dctrl_blksz(host);
 
+	if (host->hw_revision >= 3) {
+		u32 thr = 0;
+
+		if (host->mmc->ios.timing == MMC_TIMING_UHS_SDR104 ||
+		    host->mmc->ios.timing == MMC_TIMING_MMC_HS200) {
+			thr = ffs(min_t(unsigned int, host->data->blksz,
+					host->variant->fifosize));
+			thr = min_t(u32, thr, MMCI_STM32_THR_MASK);
+		}
+
+		writel_relaxed(thr, host->base + MMCI_STM32_FIFOTHRR);
+	}
+
 	if (host->mmc->card && mmc_card_sdio(host->mmc->card) &&
 	    host->data->blocks == 1)
 		datactrl |= MCI_DPSM_STM32_MODE_SDIO;