spi: rspi: Use requested instead of maximum bit rate

Currently, the RSPI driver always tries to use the maximum configured
bit rate for communicating with a slave device, even if the transfer(s)
in the current message specify a lower rate.

Use the mininum rate specified in the message instead.
Rename rspi_data.max_speed_hz accordingly.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200608095940.30516-3-geert+renesas@glider.be
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c
index 06192c9ea81329112f4aba97d0f1b0a28064c195..cbc2387d450cd4c2161599599e98335510568db6 100644 (file)
--- a/drivers/spi/spi-rspi.c
+++ b/drivers/spi/spi-rspi.c
@@ -179,7 +179,7 @@
 
 struct rspi_data {
        void __iomem *addr;
-       u32 max_speed_hz;
+       u32 speed_hz;
        struct spi_controller *ctlr;
        struct platform_device *pdev;
        wait_queue_head_t wait;
@@ -258,8 +258,7 @@ static int rspi_set_config_register(struct rspi_data *rspi, int access_size)
        rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR);
 
        /* Sets transfer bit rate */
-       spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk),
-                           2 * rspi->max_speed_hz) - 1;
+       spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk), 2 * rspi->speed_hz) - 1;
        rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR);
 
        /* Disable dummy transmission, set 16-bit word access, 1 frame */
@@ -299,14 +298,14 @@ static int rspi_rz_set_config_register(struct rspi_data *rspi, int access_size)
 
        clksrc = clk_get_rate(rspi->clk);
        while (div < 3) {
-               if (rspi->max_speed_hz >= clksrc/4) /* 4=(CLK/2)/2 */
+               if (rspi->speed_hz >= clksrc/4) /* 4=(CLK/2)/2 */
                        break;
                div++;
                clksrc /= 2;
        }
 
        /* Sets transfer bit rate */
-       spbr = DIV_ROUND_UP(clksrc, 2 * rspi->max_speed_hz) - 1;
+       spbr = DIV_ROUND_UP(clksrc, 2 * rspi->speed_hz) - 1;
        rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR);
        rspi->spcmd |= div << 2;
 
@@ -341,7 +340,7 @@ static int qspi_set_config_register(struct rspi_data *rspi, int access_size)
        rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR);
 
        /* Sets transfer bit rate */
-       spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk), 2 * rspi->max_speed_hz);
+       spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk), 2 * rspi->speed_hz);
        rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR);
 
        /* Disable dummy transmission, set byte access */
@@ -949,9 +948,24 @@ static int rspi_prepare_message(struct spi_controller *ctlr,
 {
        struct rspi_data *rspi = spi_controller_get_devdata(ctlr);
        struct spi_device *spi = msg->spi;
+       const struct spi_transfer *xfer;
        int ret;
 
-       rspi->max_speed_hz = spi->max_speed_hz;
+       /*
+        * As the Bit Rate Register must not be changed while the device is
+        * active, all transfers in a message must use the same bit rate.
+        * In theory, the sequencer could be enabled, and each Command Register
+        * could divide the base bit rate by a different value.
+        * However, most RSPI variants do not have Transfer Data Length
+        * Multiplier Setting Registers, so each sequence step would be limited
+        * to a single word, making this feature unsuitable for large
+        * transfers, which would gain most from it.
+        */
+       rspi->speed_hz = spi->max_speed_hz;
+       list_for_each_entry(xfer, &msg->transfers, transfer_list) {
+               if (xfer->speed_hz < rspi->speed_hz)
+                       rspi->speed_hz = xfer->speed_hz;
+       }
 
        rspi->spcmd = SPCMD_SSLKP;
        if (spi->mode & SPI_CPOL)