linux-kernel - Applied "spi: Clear SPI_CS_HIGH flag from bad_bits for GPIO chip-select" to the spi tree

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Message-Id: <20190427173240.59AE7441D3B@finisterre.ee.mobilebroadband>
Date:   Sat, 27 Apr 2019 18:32:40 +0100 (BST)
From:   Mark Brown <broonie@...nel.org>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
        Mark Brown <broonie@...nel.org>,
        Serge Semin <Sergey.Semin@...latforms.ru>
Subject: Applied "spi: Clear SPI_CS_HIGH flag from bad_bits for GPIO chip-select" to the spi tree

The patch

   spi: Clear SPI_CS_HIGH flag from bad_bits for GPIO chip-select

has been applied to the spi tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-5.2

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From 7f03aece72702c6204c765a2eac038eea2f3c58d Mon Sep 17 00:00:00 2001
From: Serge Semin <fancer.lancer@...il.com>
Date: Fri, 26 Apr 2019 13:30:07 +0300
Subject: [PATCH] spi: Clear SPI_CS_HIGH flag from bad_bits for GPIO
 chip-select

When GPIO chip-select is used nothing prevents any available SPI
controllers to work with both CS-high and traditional CS-low modes.
In fact the SPI bus core code already does it, so we don't need to
introduce any modification there. But spi_setup() still fails to
switch the interface settings if CS-high flag is set for the case
of GPIO-driven slave chip-select when the SPI controller doesn't
support the hardwired CS-inversion. Lets fix it by clearing the
SPI_CS_HIGH flag out from bad_bits (unsupported by controller) when
client chip is selected by GPIO.

This feature is useful for slave devices, which in accordance with
communication protocol can work with both active-high and active-low
chip-selects. I am aware of one such device. It is MMC-SPI interface,
when at init sequence the driver needs to perform a read operation with
low and high chip-select sequentially (requirement of 74 clock cycles
with both chipselect, see the mmc_spi driver for details).

Signed-off-by: Serge Semin <fancer.lancer@...il.com>
Signed-off-by: Mark Brown <broonie@...nel.org>
---
 drivers/spi/spi.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index bf4027b54a19..5be76ab68737 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2950,6 +2950,11 @@ int spi_setup(struct spi_device *spi)
 	 * so it is ignored here.
 	 */
 	bad_bits = spi->mode & ~(spi->controller->mode_bits | SPI_CS_WORD);
+	/* nothing prevents from working with active-high CS in case if it
+	 * is driven by GPIO.
+	 */
+	if (gpio_is_valid(spi->cs_gpio))
+		bad_bits &= ~SPI_CS_HIGH;
 	ugly_bits = bad_bits &
 		    (SPI_TX_DUAL | SPI_TX_QUAD | SPI_TX_OCTAL |
 		     SPI_RX_DUAL | SPI_RX_QUAD | SPI_RX_OCTAL);
-- 
2.20.1