spi: rockchip: handle zero length transfers without timing out

[ Upstream commit 5457773ef99f25fcc4b238ac76b68e28273250f4 ]

Previously zero length transfers submitted to the Rokchip SPI driver would
time out in the SPI layer. This happens because the SPI peripheral does
not trigger a transfer completion interrupt for zero length transfers.

Fix that by completing zero length transfers immediately at start of
transfer.

Signed-off-by: Tobias Schramm <t.schramm@manjaro.org>
Link: https://lore.kernel.org/r/20210827050357.165409-1-t.schramm@manjaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
index 0aab37c..624273d 100644 (file)
--- a/drivers/spi/spi-rockchip.c
+++ b/drivers/spi/spi-rockchip.c
@@ -582,6 +582,12 @@ static int rockchip_spi_transfer_one(
        int ret;
        bool use_dma;
 
+       /* Zero length transfers won't trigger an interrupt on completion */
+       if (!xfer->len) {
+               spi_finalize_current_transfer(ctlr);
+               return 1;
+       }
+
        WARN_ON(readl_relaxed(rs->regs + ROCKCHIP_SPI_SSIENR) &&
                (readl_relaxed(rs->regs + ROCKCHIP_SPI_SR) & SR_BUSY));