linux-kernel - [PATCH 0/3] spi: spi-imx: fix use of more than four chip selects

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Date:   Tue, 25 Apr 2023 15:45:24 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Mark Brown <broonie@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     Marc Kleine-Budde <mkl@...gutronix.de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH 0/3] spi: spi-imx: fix use of more than four chip selects

The current spi-imx driver completely fails when used with more than
four (gpio) chip-selects, since the chip select number is used
unconditionally as shift amount when updating the control and
configuration registers, so the code ends up modifying random bits
outside the intended fields.

This fixes it by making use of the unused_native_cs variable filled in
by the spi core, and use that as the "channel number" for all gpiod
chip selects.

In the presumably common case where all chip selects are gpios, this
means we end up using channel 0 exclusively, so the optimization where
the config register is left alone if it is unchanged (see
184434fcd617) might become less effective, if the workload consists of
different slaves with differing spi modes being accessed one after the
other. It would be nice if one could make use of the unused native
chip selects in a round-robin manner, but for that the core would have
to tell us not just unused_native_cs, but the whole ~native_cs_mask
from spi_get_gpio_descs(). Maybe a simpler fix, if there is anything
to fix, is to make the new mx51_ecspi_channel() do

	if (!spi->cs_gpiod || spi->controller->num_chipselect <= 4)

Rasmus Villemoes (3):
  spi: spi-imx: use "controller" variable consistently in
    spi_imx_probe()
  spi: spi-imx: set max_native_cs for imx51/imx53/imx6 variants
  spi: spi-imx: fix use of more than four chipselects

 drivers/spi/spi-imx.c | 56 +++++++++++++++++++++++++++----------------
 1 file changed, 35 insertions(+), 21 deletions(-)

-- 
2.37.2