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-core.c b/drivers/spi/spi-dw-core.c
index 8eb3b31b376d77791f54c028a073c0e551cf23dd..bcfa224e0e43d078f149715854288fcc7985a787 100644 (file)
--- a/drivers/spi/spi-dw-core.c
+++ b/drivers/spi/spi-dw-core.c
@@ -629,7 +629,7 @@ static int dw_spi_exec_mem_op(struct spi_mem *mem, const struct spi_mem_op *op)
         * operation. Transmit-only mode is suitable for the rest of them.
         */
        cfg.dfs = 8;
-       cfg.freq = mem->spi->max_speed_hz;
+       cfg.freq = clamp(mem->spi->max_speed_hz, 0U, dws->max_mem_freq);
        if (op->data.dir == SPI_MEM_DATA_IN) {
                cfg.tmode = SPI_TMOD_EPROMREAD;
                cfg.ndf = op->data.nbytes;
@@ -717,6 +717,8 @@ static void dw_spi_init_mem_ops(struct dw_spi *dws)
                dws->mem_ops.adjust_op_size = dw_spi_adjust_mem_op_size;
                dws->mem_ops.supports_op = dw_spi_supports_mem_op;
                dws->mem_ops.exec_op = dw_spi_exec_mem_op;
+               if (!dws->max_mem_freq)
+                       dws->max_mem_freq = dws->max_freq;
        }
 }
 

diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
index 7fadb5b963f8b1d565f02f4702dc89571a894a81..faf40cb66498dd11fb149f66c03412b7f942d610 100644 (file)
--- 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 */