On 10/11/2018 01:21 AM, Trent Piepho wrote: > On Wed, 2018-10-10 at 10:08 +0300, Talel Shenhar wrote: >> The dw spi controller has an auto-deselect of Chip-Select, in case there is >> no data inside the Tx FIFO. While working on platforms with Alpine chips, >> auto-deselect mode causes an issue for some spi devices that can't handle >> the Chip-Select deselect in the middle of a transaction. It is a normal >> behavior for a Tx FIFO to be empty in the middle of a transaction, due to >> > So that's the problem! I, like everyone else I suspect, switched to > using GPIO chip selects with this driver because of this. I narrowed > it down to a CS de-assert when the bus switched from TX to RX, which of > course makes a SPI register read fail on most devices. The TX FIFO > would empty at this point, so that would explain it. > > Did the designers of this IP ever read a SPI device datasheet??? > > Got to agree with Mark Brown, why would anyone ever want to NOT have it > work properly? The previous behavior is not "alternate correct", it's > Broken. This patch allow the Amazon changed hw to work in a correct way. Unfortunately, the original hw doesn't support auto-deselect disable. auto-deselect disable is a hw fixup Amazon hw engineers added on top of the original dw IP. The fix was to disable the auto-deselect and to allow sw to manually control the chip-select. This patch enables the above described Amazon hw fixup and adds manual control over chip-select.
