[PATCH] i2c: designware: don't infer timings described by ACPI from clock rate

[Ard Biesheuvel]

Commit bd698d24b1b57 ("i2c: designware: Get selected speed mode
sda-hold-time via ACPI") updated the logic that reads the timing
parameters for various I2C bus rates from the DSDT, to only read
the timing parameters for the currently selected mode.

This causes a WARN_ON() splat on platforms that legally omit the clock
frequency from the ACPI description, because in the new situation, the
core I2C designware driver still accesses the fields in the driver
struct that we no longer populate, and proceeds to calculate them from
the clock frequency. Since the clock frequency is unspecified, the
driver complains loudly using a WARN_ON().

So revert back to the old situation, where the struct fields for all
timings are populated, but retain the new logic which chooses the SDA
hold time from the timing mode that is currently in use.

Fixes: bd698d24b1b57 ("i2c: designware: Get selected speed mode ...")
Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
 drivers/i2c/busses/i2c-designware-platdrv.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
index f2acd4b6bf01..6283b99d2b17 100644
--- a/drivers/i2c/busses/i2c-designware-platdrv.c
+++ b/drivers/i2c/busses/i2c-designware-platdrv.c
@@ -96,6 +96,7 @@ static int dw_i2c_acpi_configure(struct platform_device *pdev)
 	struct dw_i2c_dev *dev = platform_get_drvdata(pdev);
 	acpi_handle handle = ACPI_HANDLE(&pdev->dev);
 	const struct acpi_device_id *id;
+	u32 ss_ht, fp_ht, hs_ht, fs_ht;
 	struct acpi_device *adev;
 	const char *uid;
 
@@ -107,23 +108,24 @@ static int dw_i2c_acpi_configure(struct platform_device *pdev)
 	 * Try to get SDA hold time and *CNT values from an ACPI method for
 	 * selected speed modes.
 	 */
+	dw_i2c_acpi_params(pdev, "SSCN", &dev->ss_hcnt, &dev->ss_lcnt, &ss_ht);
+	dw_i2c_acpi_params(pdev, "FPCN", &dev->fp_hcnt, &dev->fp_lcnt, &fp_ht);
+	dw_i2c_acpi_params(pdev, "HSCN", &dev->hs_hcnt, &dev->hs_lcnt, &hs_ht);
+	dw_i2c_acpi_params(pdev, "FMCN", &dev->fs_hcnt, &dev->fs_lcnt, &fs_ht);
+
 	switch (dev->clk_freq) {
 	case 100000:
-		dw_i2c_acpi_params(pdev, "SSCN", &dev->ss_hcnt, &dev->ss_lcnt,
-				   &dev->sda_hold_time);
+		dev->sda_hold_time = ss_ht;
 		break;
 	case 1000000:
-		dw_i2c_acpi_params(pdev, "FPCN", &dev->fp_hcnt, &dev->fp_lcnt,
-				   &dev->sda_hold_time);
+		dev->sda_hold_time = fp_ht;
 		break;
 	case 3400000:
-		dw_i2c_acpi_params(pdev, "HSCN", &dev->hs_hcnt, &dev->hs_lcnt,
-				   &dev->sda_hold_time);
+		dev->sda_hold_time = hs_ht;
 		break;
 	case 400000:
 	default:
-		dw_i2c_acpi_params(pdev, "FMCN", &dev->fs_hcnt, &dev->fs_lcnt,
-				   &dev->sda_hold_time);
+		dev->sda_hold_time = fs_ht;
 		break;
 	}
 
-- 
2.9.3