linux-kernel - [PATCH] spi: rockchip: handle zero length transfers without timing out

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Date:   Fri, 27 Aug 2021 07:03:57 +0200
From:   Tobias Schramm <t.schramm@...jaro.org>
To:     linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Mark Brown <broonie@...nel.org>, Heiko Stuebner <heiko@...ech.de>,
        Tobias Schramm <t.schramm@...jaro.org>
Subject: [PATCH] spi: rockchip: handle zero length transfers without timing out

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@...jaro.org>
---
 drivers/spi/spi-rockchip.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
index 540861ca2ba3..553b6b9d0222 100644
--- a/drivers/spi/spi-rockchip.c
+++ b/drivers/spi/spi-rockchip.c
@@ -600,6 +600,12 @@ 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));
 
-- 
2.33.0