[PATCH v3 1/2] mmc: host: sdhci-esdhc-imx: implement emmc hardware reset

[Josua Mayer <josua@solid-run.com>]

NXP ESDHC supports control of native emmc reset signal when pinmux is
set accordingly, using uSDHCx_SYS_CTRL register IPP_RST_N bit.
Documentation is available in NXP i.MX6Q Reference Manual.

Implement the hw_reset function in sdhci_ops asserting reset for at
least 1us and waiting at least 200us after deassertion.
Lower bounds are based on:
JEDEC Standard No. 84-B51, 6.15.10 H/W Reset Operation, page 159.
Upper bounds are chosen allowing flexibility to the scheduler.

Tested on SolidRun i.MX8DXL SoM with a scope, and confirmed that eMMC is
still accessible after boot:
- eMMC extcsd has RST_N_FUNCTION=0x01
- sdhc node has cap-mmc-hw-reset
- pinmux set for EMMC0_RESET_B
- Linux v5.15

Signed-off-by: Josua Mayer <josua@solid-run.com>
---
 drivers/mmc/host/sdhci-esdhc-imx.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-esdhc-imx.c
index 8f0bc6dca2b0402fd2a0695903cf261a5b4e19dc..f106e291c276d0c8063e9ac59a126acf5e9e239e 100644
--- a/drivers/mmc/host/sdhci-esdhc-imx.c
+++ b/drivers/mmc/host/sdhci-esdhc-imx.c
@@ -31,6 +31,7 @@
 #include "cqhci.h"
 
 #define ESDHC_SYS_CTRL_DTOCV_MASK	0x0f
+#define ESDHC_SYS_CTRL_IPP_RST_N	BIT(23)
 #define	ESDHC_CTRL_D3CD			0x08
 #define ESDHC_BURST_LEN_EN_INCR		(1 << 27)
 /* VENDOR SPEC register */
@@ -1402,6 +1403,17 @@ static u32 esdhc_cqhci_irq(struct sdhci_host *host, u32 intmask)
 	return 0;
 }
 
+static void esdhc_hw_reset(struct sdhci_host *host)
+{
+	esdhc_clrset_le(host, ESDHC_SYS_CTRL_IPP_RST_N, 0, ESDHC_SYSTEM_CONTROL);
+	/* eMMC spec requires minimum 1us, here delay between 1-10us */
+	usleep_range(1, 10);
+	esdhc_clrset_le(host, ESDHC_SYS_CTRL_IPP_RST_N,
+			ESDHC_SYS_CTRL_IPP_RST_N, ESDHC_SYSTEM_CONTROL);
+	/* eMMC spec requires minimum 200us, here delay between 200-300us */
+	usleep_range(200, 300);
+}
+
 static struct sdhci_ops sdhci_esdhc_ops = {
 	.read_l = esdhc_readl_le,
 	.read_w = esdhc_readw_le,
@@ -1420,6 +1432,7 @@ static struct sdhci_ops sdhci_esdhc_ops = {
 	.reset = esdhc_reset,
 	.irq = esdhc_cqhci_irq,
 	.dump_vendor_regs = esdhc_dump_debug_regs,
+	.hw_reset = esdhc_hw_reset,
 };
 
 static const struct sdhci_pltfm_data sdhci_esdhc_imx_pdata = {

-- 
2.43.0