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>
1 file changed