spi: rzv2h-rspi: add support for loopback mode

Add support for loopback mode for debugging purposes, allowing us to
test the SPI controller at the maximum SPI transfer clock without being
limited by external wiring.

Signed-off-by: Cosmin Tanislav <cosmin-gabriel.tanislav.xa@renesas.com>
Link: https://patch.msgid.link/20251119161434.595677-10-cosmin-gabriel.tanislav.xa@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-rzv2h-rspi.c b/drivers/spi/spi-rzv2h-rspi.c
index be45269e885384e023a8dd6cd748201533ce762b..da110efba971e1fe68d5a54d9be66acbb8e6f437 100644 (file)
--- a/drivers/spi/spi-rzv2h-rspi.c
+++ b/drivers/spi/spi-rzv2h-rspi.c
@@ -24,6 +24,7 @@
 /* Registers */
 #define RSPI_SPDR              0x00
 #define RSPI_SPCR              0x08
+#define RSPI_SPPCR             0x0e
 #define RSPI_SSLP              0x10
 #define RSPI_SPBR              0x11
 #define RSPI_SPSCR             0x13
@@ -40,6 +41,9 @@
 #define RSPI_SPCR_SCKASE       BIT(12)
 #define RSPI_SPCR_SPE          BIT(0)
 
+/* Register SPPCR */
+#define RSPI_SPPCR_SPLP2       BIT(1)
+
 /* Register SPBR */
 #define RSPI_SPBR_SPR_MIN      0
 #define RSPI_SPBR_SPR_PCLK_MIN 1
@@ -345,6 +349,7 @@ static int rzv2h_rspi_prepare_message(struct spi_controller *ctlr,
        u8 bits_per_word;
        u32 conf32;
        u16 conf16;
+       u8 conf8;
 
        /* Make sure SPCR.SPE is 0 before amending the configuration */
        rzv2h_rspi_spe_disable(rspi);
@@ -389,6 +394,10 @@ static int rzv2h_rspi_prepare_message(struct spi_controller *ctlr,
        /* Use SPCMD0 only */
        writeb(0x0, rspi->base + RSPI_SPSCR);
 
+       /* Setup loopback */
+       conf8 = FIELD_PREP(RSPI_SPPCR_SPLP2, !!(spi->mode & SPI_LOOP));
+       writeb(conf8, rspi->base + RSPI_SPPCR);
+
        /* Setup mode */
        conf32 = FIELD_PREP(RSPI_SPCMD_CPOL, !!(spi->mode & SPI_CPOL));
        conf32 |= FIELD_PREP(RSPI_SPCMD_CPHA, !!(spi->mode & SPI_CPHA));
@@ -490,7 +499,7 @@ static int rzv2h_rspi_probe(struct platform_device *pdev)
        }
 
        controller->mode_bits = SPI_CPHA | SPI_CPOL | SPI_CS_HIGH |
-                               SPI_LSB_FIRST;
+                               SPI_LSB_FIRST | SPI_LOOP;
        controller->bits_per_word_mask = SPI_BPW_RANGE_MASK(4, 32);
        controller->prepare_message = rzv2h_rspi_prepare_message;
        controller->unprepare_message = rzv2h_rspi_unprepare_message;