[PATCH v3] spi: spi-imx: Fix spi_bus_clk if requested clock is higher than input clock

From: Frieder Schrempf <frieder@fris.de>
To: David Jander <david@protonic.nl>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-spi@vger.kernel.org,
	Marc Kleine-Budde <mkl@pengutronix.de>,
	Marek Vasut <marex@denx.de>, Mark Brown <broonie@kernel.org>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	Shawn Guo <shawnguo@kernel.org>
Cc: Frieder Schrempf <frieder.schrempf@kontron.de>,
	Fabio Estevam <festevam@gmail.com>,
	stable@vger.kernel.org, Baruch Siach <baruch.siach@siklu.com>,
	Minghao Chi <chi.minghao@zte.com.cn>,
	NXP Linux Team <linux-imx@nxp.com>,
	Pengutronix Kernel Team <kernel@pengutronix.de>
Subject: [PATCH v3] spi: spi-imx: Fix spi_bus_clk if requested clock is higher than input clock
Date: Tue, 15 Nov 2022 19:10:00 +0100	[thread overview]
Message-ID: <20221115181002.2068270-1-frieder@fris.de> (raw)

From: Frieder Schrempf <frieder.schrempf@kontron.de>

In case the requested bus clock is higher than the input clock, the correct
dividers (pre = 0, post = 0) are returned from mx51_ecspi_clkdiv(), but
*fres is left uninitialized and therefore contains an arbitrary value.

This causes trouble for the recently introduced PIO polling feature as the
value in spi_imx->spi_bus_clk is used there to calculate for which
transfers to enable PIO polling.

Fix this by setting *fres even if no clock dividers are in use.

This issue was observed on Kontron BL i.MX8MM with an SPI peripheral clock set
to 50 MHz by default and a requested SPI bus clock of 80 MHz for the SPI NOR
flash.

With the fix applied the debug message from mx51_ecspi_clkdiv() now prints the
following:

spi_imx 30820000.spi: mx51_ecspi_clkdiv: fin: 50000000, fspi: 50000000,
post: 0, pre: 0

Fixes: 6fd8b8503a0d ("spi: spi-imx: Fix out-of-order CS/SCLK operation at low speeds")
Fixes: 07e759387788 ("spi: spi-imx: add PIO polling support")
Cc: Marc Kleine-Budde <mkl@pengutronix.de>
Cc: David Jander <david@protonic.nl>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Marek Vasut <marex@denx.de>
Cc: stable@vger.kernel.org
Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Tested-by: Fabio Estevam <festevam@gmail.com>
---

Changes for v3:

* Add back the Fixes tag for commit 6fd8b8503a0d
* Add Fabio's Tested-by (Thanks!)

Changes for v2:

* Remove the reference and the Fixes tag for commit 6fd8b8503a0d as it is
  incorrect.
---
 drivers/spi/spi-imx.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
index 30d82cc7300b..468ce0a2b282 100644
--- a/drivers/spi/spi-imx.c
+++ b/drivers/spi/spi-imx.c
@@ -444,8 +444,7 @@ static unsigned int mx51_ecspi_clkdiv(struct spi_imx_data *spi_imx,
 	unsigned int pre, post;
 	unsigned int fin = spi_imx->spi_clk;
 
-	if (unlikely(fspi > fin))
-		return 0;
+	fspi = min(fspi, fin);
 
 	post = fls(fin) - fls(fspi);
 	if (fin > fspi << post)
-- 
2.38.1

