The current use of the mode flag SPI_CS_HIGH is fragile: it
overwrites anything already assigned by the SPI core.
Assign ^= SPI_CS_HIGH since we might be active high
already, and that is usually the case with GPIOs used
for chip select, even if they are in practice active low.
Add a comment clarifying why ^= SPI_CS_HIGH is the right
choice here.
Reported-by: Mark Brown <broo...@kernel.org>
Signed-off-by: Linus Walleij <linus.wall...@linaro.org>
---
drivers/staging/fbtft/fb_uc1611.c | 12 +++++++++---
drivers/staging/fbtft/fb_watterott.c | 13 ++++++++++---
2 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/drivers/staging/fbtft/fb_uc1611.c
b/drivers/staging/fbtft/fb_uc1611.c
index e763205e9e4f..f61e373c75e9 100644
--- a/drivers/staging/fbtft/fb_uc1611.c
+++ b/drivers/staging/fbtft/fb_uc1611.c
@@ -63,11 +63,17 @@ static int init_display(struct fbtft_par *par)
{
int ret;
- /* Set CS active high */
- par->spi->mode |= SPI_CS_HIGH;
+ /*
+ * Set CS active inverse polarity: just setting SPI_CS_HIGH does not
+ * work with GPIO based chip selects that are logically active high
+ * but inverted inside the GPIO library, so enforce inverted
+ * semantics.
+ */
+ par->spi->mode ^= SPI_CS_HIGH;
ret = spi_setup(par->spi);
if (ret) {
- dev_err(par->info->device, "Could not set SPI_CS_HIGH\n");
+ dev_err(par->info->device,
+ "Could not set inverse CS polarity\n");
return ret;
}
diff --git a/drivers/staging/fbtft/fb_watterott.c
b/drivers/staging/fbtft/fb_watterott.c
index 27cc8eabcbe9..76b25df376b8 100644
--- a/drivers/staging/fbtft/fb_watterott.c
+++ b/drivers/staging/fbtft/fb_watterott.c
@@ -150,10 +150,17 @@ static int init_display(struct fbtft_par *par)
/* enable SPI interface by having CS and MOSI low during reset */
save_mode = par->spi->mode;
- par->spi->mode |= SPI_CS_HIGH;
- ret = spi_setup(par->spi); /* set CS inactive low */
+ /*
+ * Set CS active inverse polarity: just setting SPI_CS_HIGH does not
+ * work with GPIO based chip selects that are logically active high
+ * but inverted inside the GPIO library, so enforce inverted
+ * semantics.
+ */
+ par->spi->mode ^= SPI_CS_HIGH;
+ ret = spi_setup(par->spi);
if (ret) {
- dev_err(par->info->device, "Could not set SPI_CS_HIGH\n");
+ dev_err(par->info->device,
+ "Could not set inverse CS polarity\n");
return ret;
}
write_reg(par, 0x00); /* make sure mode is set */
--
2.23.0
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