netdev - [PATCH net v2] net: phy: spi_ks8995: Do not overwrite SPI mode flags

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Date:   Tue, 10 Nov 2020 09:20:32 -0500
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Sven Van Asbroeck <thesven73@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Frederic LAMBERT <frdrc66@...il.com>,
        Gabor Juhos <juhosg@...nwrt.org>,
        Jonathan Cameron <jonathan.cameron@...wei.com>,
        linux-spi@...r.kernel.org
Subject: [PATCH net v2] net: phy: spi_ks8995: Do not overwrite SPI mode flags

From: Sven Van Asbroeck <thesven73@...il.com>

This driver makes sure the underlying SPI bus is set to "mode 0"
by assigning SPI_MODE_0 to spi->mode. Which overwrites all other
SPI mode flags.

In some circumstances, this can break the underlying SPI bus driver.
For example, if SPI_CS_HIGH is set on the SPI bus, the driver
will clear that flag, which results in a chip-select polarity issue.

Fix by changing only the SPI_MODE_N bits, i.e. SPI_CPHA and SPI_CPOL.

Fixes: a8e510f682fe ("phy: Micrel KS8995MA 5-ports 10/100 managed Ethernet switch support added")
Fixes: f3186dd87669 ("spi: Optionally use GPIO descriptors for CS GPIOs")
Link: https://patchwork.kernel.org/project/spi-devel-general/patch/20201106150706.29089-1-TheSven73@gmail.com/#23747737
Signed-off-by: Sven Van Asbroeck <thesven73@...il.com>
---

Tree: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git # 989ef49bdf10

To be followed by a proposed spi helper function. Submit to net-next after net
gets merged into net-next.

# large number of people, from get_maintainer.pl
To: Andrew Lunn <andrew@...n.ch>
To: Heiner Kallweit <hkallweit1@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Russell King <linux@...linux.org.uk>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org

Cc: Mark Brown <broonie@...nel.org>
Cc: Linus Walleij <linus.walleij@...aro.org>
Cc: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Frederic LAMBERT <frdrc66@...il.com>
Cc: Gabor Juhos <juhosg@...nwrt.org>
Cc: Jonathan Cameron <jonathan.cameron@...wei.com>

# Cc SPI group, suggested by Jakub Kicinski
Cc: linux-spi@...r.kernel.org

 drivers/net/phy/spi_ks8995.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/spi_ks8995.c b/drivers/net/phy/spi_ks8995.c
index 4b198399bfa2..3c6c87a09b03 100644
--- a/drivers/net/phy/spi_ks8995.c
+++ b/drivers/net/phy/spi_ks8995.c
@@ -491,7 +491,9 @@ static int ks8995_probe(struct spi_device *spi)
 
 	spi_set_drvdata(spi, ks);
 
-	spi->mode = SPI_MODE_0;
+	/* use SPI_MODE_0 without changing any other mode flags */
+	spi->mode &= ~(SPI_CPHA | SPI_CPOL);
+	spi->mode |= SPI_MODE_0;
 	spi->bits_per_word = 8;
 	err = spi_setup(spi);
 	if (err) {
-- 
2.17.1