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56 lines
2.3 KiB
Diff
56 lines
2.3 KiB
Diff
From b4659f44df3454c6b37ba206a0347af3b8d6a744 Mon Sep 17 00:00:00 2001
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From: Phil Elwell <phil@raspberrypi.com>
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Date: Mon, 20 Apr 2020 13:30:49 +0100
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Subject: [PATCH] spi: use_gpio_descriptor fixup moved to spi_setup
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Commits [1] and [2] including code that forces SPI_CS_HIGH for SPI
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controllers that use GPIO descriptors, the SPI_CS_HIGH flag being
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there to avoid a double-negation (since SPI CS is usually active-low).
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The motivation for pushing the knowledge of the required polarity into
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the GPIO descriptor allows the switch to an output to request the
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correct inactive level, avoiding a needless glitch.
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The problem with setting the flag early as [1] does is that it appears
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in the mode field that is passed to client drivers during their probing,
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when they may want to choose SPI_POL, SPI_PHA and (just possibly)
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SPI_CS_HIGH. Since SPI_CS_HIGH is the exception, most drivers won't
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set it and the anti-negation negation is lost. [2] acknowledges that
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problem and patches things up for the case of users of spidev, but
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omits regular kernel-mode drivers.
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Downstream commit [3] moves the forcing of SPI_CS_HIGH to spi_setup,
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after the driver probing. Since this code is called before any CS
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manipulation it is early enough to be effective, but late enough that
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clients have already had their chance to change the mode field.
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This is a partial reversion of [1], and is accompanied by a complete
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reversion of [2], neither of which is needed any longer.
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[1] f3186dd87669 ("spi: Optionally use GPIO descriptors for CS GPIOs")
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[2] 83b2a8fe43bd ("spi: spidev: Fix CS polarity if GPIO descriptors are used")
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[3] <varies> ("spi: Force CS_HIGH if GPIO descriptors are used")
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Signed-off-by: Phil Elwell <phil@raspberrypi.com>
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---
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drivers/spi/spi.c | 9 ---------
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1 file changed, 9 deletions(-)
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--- a/drivers/spi/spi.c
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+++ b/drivers/spi/spi.c
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@@ -1775,15 +1775,6 @@ static int of_spi_parse_dt(struct spi_co
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}
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spi->chip_select = value;
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- /*
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- * For descriptors associated with the device, polarity inversion is
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- * handled in the gpiolib, so all gpio chip selects are "active high"
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- * in the logical sense, the gpiolib will invert the line if need be.
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- */
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- if ((ctlr->use_gpio_descriptors) && ctlr->cs_gpiods &&
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- ctlr->cs_gpiods[spi->chip_select])
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- spi->mode |= SPI_CS_HIGH;
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-
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/* Device speed */
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rc = of_property_read_u32(nc, "spi-max-frequency", &value);
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if (rc) {
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