spi: dw: Introduce max mem-ops SPI bus frequency setting
In some circumstances the current implementation of the SPI memory
operations may occasionally fail even though they are executed in the
atomic context. This may happen if the system bus is relatively slow in
comparison to the SPI bus frequency, or there is a concurrent access to
it, which makes the MMIO-operations occasionally stalling before
push-pulling data from the DW APB SPI FIFOs. These two problems we've
discovered on the Baikal-T1 SoC. In order to fix them we have no choice
but to set an artificial limitation on the SPI bus speed.
Note currently this limitation will be only applicable for the memory
operations, since the standard SPI core interface is implemented with an
assumption that there is no problem with the automatic CS toggling.
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20201007235511.4935-19-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
index 7fadb5b..faf40cb 100644
--- a/drivers/spi/spi-dw.h
+++ b/drivers/spi/spi-dw.h
@@ -148,6 +148,7 @@ struct dw_spi {
unsigned long paddr;
int irq;
u32 fifo_len; /* depth of the FIFO buffer */
+ u32 max_mem_freq; /* max mem-ops bus freq */
u32 max_freq; /* max bus freq supported */
u32 caps; /* DW SPI capabilities */
