[PATCH] 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 10us and waiting an extra 300us after deassertion.
These particular delays were inspired by sunxi-mmc hw_reset function.

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, i.e.
reset input enabled, Linux v5.15.

Signed-off-by: Josua Mayer <josua@solid-run.com>
---
 drivers/mmc/host/sdhci-esdhc-imx.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-esdhc-imx.c
index 8f0bc6dca2b0402fd2a0695903cf261a5b4e19dc..ebcfa427cca6cc2791a1701a3515ef6515779aa4 100644
--- a/drivers/mmc/host/sdhci-esdhc-imx.c
+++ b/drivers/mmc/host/sdhci-esdhc-imx.c
@@ -33,6 +33,8 @@
 #define ESDHC_SYS_CTRL_DTOCV_MASK	0x0f
 #define	ESDHC_CTRL_D3CD			0x08
 #define ESDHC_BURST_LEN_EN_INCR		(1 << 27)
+#define ESDHC_SYS_CTRL			0x2c
+#define ESDHC_SYS_CTRL_IPP_RST_N	BIT(23)
 /* VENDOR SPEC register */
 #define ESDHC_VENDOR_SPEC		0xc0
 #define  ESDHC_VENDOR_SPEC_SDIO_QUIRK	(1 << 1)
@@ -1402,6 +1404,15 @@ 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_SYS_CTRL);
+	udelay(10);
+	esdhc_clrset_le(host, ESDHC_SYS_CTRL_IPP_RST_N,
+			ESDHC_SYS_CTRL_IPP_RST_N, ESDHC_SYS_CTRL);
+	udelay(300);
+}
+
 static struct sdhci_ops sdhci_esdhc_ops = {
 	.read_l = esdhc_readl_le,
 	.read_w = esdhc_readw_le,
@@ -1420,6 +1431,7 @@ 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 = {

---
base-commit: 9852d85ec9d492ebef56dc5f229416c925758edc
change-id: 20241027-imx-emmc-reset-7127d311174c

Best regards,
-- 
Josua Mayer <josua@solid-run.com>