spi: Use Apple device properties in absence of ACPI resources
authorLukas Wunner <lukas@wunner.de>
Tue, 1 Aug 2017 12:10:41 +0000 (14:10 +0200)
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>
Thu, 3 Aug 2017 21:26:23 +0000 (23:26 +0200)
commit8a2e487e6fc1dddd406175c1f99a733f4a1206e2
tree5136589a7dc63e8b43b306cf1233b8468868a37c
parentca9ef3ab68d3530ac93d4254f9e47724ea51758d
spi: Use Apple device properties in absence of ACPI resources

MacBooks and MacBook Pros introduced since 2015 return empty _CRS data
for SPI slaves, causing device initialization to fail.  Most of the
information that would normally be conveyed via _CRS is available
through ACPI device properties instead, so take advantage of them.

The meaning and appropriate usage of the device properties was reverse
engineered by Ronald Tschalär and carried over from these commits
authored by him:

https://github.com/cb22/macbook12-spi-driver/commit/9a416d699ef4
https://github.com/cb22/macbook12-spi-driver/commit/0c34936ed9a1

According to Ronald, the device properties have the following meaning:

spiSclkPeriod   /* period in ns */
spiWordSize     /* in number of bits */
spiBitOrder     /* 1 = MSB_FIRST, 0 = LSB_FIRST */
spiSPO          /* clock polarity: 0 = low, 1 = high */
spiSPH          /* clock phase: 0 = first, 1 = second */
spiCSDelay      /* delay between cs and receive on reads in 10 us */
resetA2RUsec    /* active-to-receive delay? */
resetRecUsec    /* receive delay? */

Reported-by: Leif Liddy <leif.liddy@gmail.com>
Tested-by: Ronald Tschalär <ronald@innovation.ch>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
drivers/spi/spi.c