mmc: sdhci-pci: Quirk for AMD SDHC Device 0x7906

AMD SDHC 0x7906 requires a hard reset to clear all internal state.
Otherwise it can get into a bad state where the DATA lines are always
read as zeros.

This change requires firmware that can transition the device into
D3Cold for it to work correctly. If the firmware does not support
transitioning to D3Cold then the power state transitions are a no-op.

Signed-off-by: Raul E Rangel <[e-mail]>
Signed-off-by: Shyam Sundar S K <[e-mail]>
Acked-by: Adrian Hunter <[e-mail]>
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/host/sdhci-pci-core.c

···
 #include <linux/mmc/mmc.h>
 #include <linux/scatterlist.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/gpio.h>
 #include <linux/pm_runtime.h>
 #include <linux/mmc/slot-gpio.h>
···
 	return 0;
 }
 
+static u32 sdhci_read_present_state(struct sdhci_host *host)
+{
+	return sdhci_readl(host, SDHCI_PRESENT_STATE);
+}
+
+void amd_sdhci_reset(struct sdhci_host *host, u8 mask)
+{
+	struct sdhci_pci_slot *slot = sdhci_priv(host);
+	struct pci_dev *pdev = slot->chip->pdev;
+	u32 present_state;
+
+	/*
+	 * SDHC 0x7906 requires a hard reset to clear all internal state.
+	 * Otherwise it can get into a bad state where the DATA lines are always
+	 * read as zeros.
+	 */
+	if (pdev->device == 0x7906 && (mask & SDHCI_RESET_ALL)) {
+		pci_clear_master(pdev);
+
+		pci_save_state(pdev);
+
+		pci_set_power_state(pdev, PCI_D3cold);
+		pr_debug("%s: power_state=%u\n", mmc_hostname(host->mmc),
+			pdev->current_state);
+		pci_set_power_state(pdev, PCI_D0);
+
+		pci_restore_state(pdev);
+
+		/*
+		 * SDHCI_RESET_ALL says the card detect logic should not be
+		 * reset, but since we need to reset the entire controller
+		 * we should wait until the card detect logic has stabilized.
+		 *
+		 * This normally takes about 40ms.
+		 */
+		readx_poll_timeout(
+			sdhci_read_present_state,
+			host,
+			present_state,
+			present_state & SDHCI_CD_STABLE,
+			10000,
+			100000
+		);
+	}
+
+	return sdhci_reset(host, mask);
+}
+
 static const struct sdhci_ops amd_sdhci_pci_ops = {
 	.set_clock			= sdhci_set_clock,
 	.enable_dma			= sdhci_pci_enable_dma,
 	.set_bus_width			= sdhci_set_bus_width,
-	.reset				= sdhci_reset,
+	.reset				= amd_sdhci_reset,
 	.set_uhs_signaling		= sdhci_set_uhs_signaling,
 };