[RFC 2/2] mmc: sdhci-pci: Use ACPI to get max frequency for Intel byt sdio host controller sub-vended by NI

[Zach Brown]

On NI 9037 boards the max SDIO frequency is limited by trace lengths
and other layout choices. The max SDIO frequency is stored in an ACPI
table, as MXFQ.

The driver reads the ACPI entry MXFQ during sdio_probe_slot and sets the
f_max field of the host with it.

Signed-off-by: Nathan Sullivan <nathan.sullivan@xxxxxx>
Reviewed-by: Jaeden Amero <jaeden.amero@xxxxxx>
Reviewed-by: Josh Cartwright <joshc@xxxxxx>
Signed-off-by: Zach Brown <zach.brown@xxxxxx>
---
 drivers/mmc/host/sdhci-pci-core.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/mmc/host/sdhci-pci-core.c b/drivers/mmc/host/sdhci-pci-core.c
index c333ce2..4ac7f16 100644
--- a/drivers/mmc/host/sdhci-pci-core.c
+++ b/drivers/mmc/host/sdhci-pci-core.c
@@ -27,6 +27,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/mmc/slot-gpio.h>
 #include <linux/mmc/sdhci-pci-data.h>
+#include <linux/acpi.h>
 
 #include "sdhci.h"
 #include "sdhci-pci.h"
@@ -377,6 +378,35 @@ static int byt_emmc_probe_slot(struct sdhci_pci_slot *slot)
 
 static int ni_byt_sdio_probe_slot(struct sdhci_pci_slot *slot)
 {
+#ifdef CONFIG_ACPI
+	/* Get max freq from ACPI for NI hardware */
+	acpi_handle acpi_hdl;
+	acpi_status status;
+	struct acpi_buffer acpi_result = {
+		ACPI_ALLOCATE_BUFFER, NULL };
+	union acpi_object *acpi_buffer;
+	int max_freq;
+
+	status = acpi_get_handle(ACPI_HANDLE(&slot->chip->pdev->dev), "MXFQ",
+				 &acpi_hdl);
+	if (ACPI_FAILURE(status))
+		return  -ENODEV;
+
+	status = acpi_evaluate_object(acpi_hdl, NULL,
+				      NULL, &acpi_result);
+	if (ACPI_FAILURE(status))
+		return -EINVAL;
+
+	acpi_buffer = (union acpi_object *)acpi_result.pointer;
+
+	if (acpi_buffer->type != ACPI_TYPE_INTEGER)
+		return -EINVAL;
+
+	max_freq = acpi_buffer->integer.value;
+
+	slot->host->mmc->f_max = max_freq * 1000000;
+#endif
+
 	slot->host->mmc->caps |= MMC_CAP_POWER_OFF_CARD | MMC_CAP_NONREMOVABLE;
 	return 0;
 }
-- 
2.7.4