Raul E Rangel e10f480902 mmc: sdhci-acpi: AMDI0040: Allow changing HS200/HS400 driver strength ...

This change will allow platform designers better control over signal
integrity by allowing them to tune the HS200 and HS400 driver strengths.

The driver strength was previously hard coded to A to solve boot
problems with certain platforms. This driver strength does not
universally apply to all platforms so we need a knob to adjust it.

All older platforms currently have the SDR104 preset hard coded to A in
the firmware. This means that switching from the hard coded value in
the kernel to reading the SDR104 preset is a no-op for these platforms.
Newer platforms will have properly set presets. So this change will
support both new and old platforms.

Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Signed-off-by: Victor Ding <victording@google.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20201027084612.528301-1-victording@google.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

2020-11-16 11:59:27 +01:00

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