diff options
Diffstat (limited to 'target/linux/bcm27xx/patches-5.4/950-0665-spi-use_gpio_descriptor-fixup-moved-to-spi_setup.patch')
-rw-r--r-- | target/linux/bcm27xx/patches-5.4/950-0665-spi-use_gpio_descriptor-fixup-moved-to-spi_setup.patch | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/target/linux/bcm27xx/patches-5.4/950-0665-spi-use_gpio_descriptor-fixup-moved-to-spi_setup.patch b/target/linux/bcm27xx/patches-5.4/950-0665-spi-use_gpio_descriptor-fixup-moved-to-spi_setup.patch new file mode 100644 index 0000000000..8792faa0c9 --- /dev/null +++ b/target/linux/bcm27xx/patches-5.4/950-0665-spi-use_gpio_descriptor-fixup-moved-to-spi_setup.patch @@ -0,0 +1,55 @@ +From b4659f44df3454c6b37ba206a0347af3b8d6a744 Mon Sep 17 00:00:00 2001 +From: Phil Elwell <phil@raspberrypi.com> +Date: Mon, 20 Apr 2020 13:30:49 +0100 +Subject: [PATCH] spi: use_gpio_descriptor fixup moved to spi_setup + +Commits [1] and [2] including code that forces SPI_CS_HIGH for SPI +controllers that use GPIO descriptors, the SPI_CS_HIGH flag being +there to avoid a double-negation (since SPI CS is usually active-low). +The motivation for pushing the knowledge of the required polarity into +the GPIO descriptor allows the switch to an output to request the +correct inactive level, avoiding a needless glitch. + +The problem with setting the flag early as [1] does is that it appears +in the mode field that is passed to client drivers during their probing, +when they may want to choose SPI_POL, SPI_PHA and (just possibly) +SPI_CS_HIGH. Since SPI_CS_HIGH is the exception, most drivers won't +set it and the anti-negation negation is lost. [2] acknowledges that +problem and patches things up for the case of users of spidev, but +omits regular kernel-mode drivers. + +Downstream commit [3] moves the forcing of SPI_CS_HIGH to spi_setup, +after the driver probing. Since this code is called before any CS +manipulation it is early enough to be effective, but late enough that +clients have already had their chance to change the mode field. + +This is a partial reversion of [1], and is accompanied by a complete +reversion of [2], neither of which is needed any longer. + +[1] f3186dd87669 ("spi: Optionally use GPIO descriptors for CS GPIOs") +[2] 83b2a8fe43bd ("spi: spidev: Fix CS polarity if GPIO descriptors are used") +[3] <varies> ("spi: Force CS_HIGH if GPIO descriptors are used") + +Signed-off-by: Phil Elwell <phil@raspberrypi.com> +--- + drivers/spi/spi.c | 9 --------- + 1 file changed, 9 deletions(-) + +--- a/drivers/spi/spi.c ++++ b/drivers/spi/spi.c +@@ -1793,15 +1793,6 @@ static int of_spi_parse_dt(struct spi_co + } + spi->chip_select = value; + +- /* +- * For descriptors associated with the device, polarity inversion is +- * handled in the gpiolib, so all gpio chip selects are "active high" +- * in the logical sense, the gpiolib will invert the line if need be. +- */ +- if ((ctlr->use_gpio_descriptors) && ctlr->cs_gpiods && +- ctlr->cs_gpiods[spi->chip_select]) +- spi->mode |= SPI_CS_HIGH; +- + /* Device speed */ + rc = of_property_read_u32(nc, "spi-max-frequency", &value); + if (rc) { |