| Message ID | 20221116-s905x_spi_ili9486-v2-2-084c6e3cd930@baylibre.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Make ILI9486 driver working with 16-bits SPI controllers | expand |
On 21/11/2022 10:42, Carlo Caione wrote: > The pixel data for the ILI9486 is always 16-bits wide and it must be > sent over the SPI bus. When the controller is only able to deal with > 8-bit transfers, this 16-bits data needs to be swapped before the > sending to account for the big endian bus, this is on the contrary not > needed when the SPI controller already supports 16-bits transfers. > > The decision about swapping the pixel data or not is taken in the MIPI > DBI code by probing the controller capabilities: if the controller only > suppors 8-bit transfers the data is swapped, otherwise it is not. > > This swapping/non-swapping is relying on the assumption that when the > controller does support 16-bit transactions then the data is sent > unswapped in 16-bits-per-word over SPI. > > The problem with the ILI9486 driver is that it is forcing 8-bit > transactions also for controllers supporting 16-bits, violating the > assumption and corrupting the pixel data. > > Align the driver to what is done in the MIPI DBI code by adjusting the > tranfer size to the maximum allowed by the SPI controller. > > Signed-off-by: Carlo Caione <ccaione@baylibre.com> > --- > drivers/gpu/drm/tiny/ili9486.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/tiny/ili9486.c b/drivers/gpu/drm/tiny/ili9486.c > index bd37dfe8dd05..4d80a413338f 100644 > --- a/drivers/gpu/drm/tiny/ili9486.c > +++ b/drivers/gpu/drm/tiny/ili9486.c > @@ -43,6 +43,7 @@ static int waveshare_command(struct mipi_dbi *mipi, u8 *cmd, u8 *par, > size_t num) > { > struct spi_device *spi = mipi->spi; > + unsigned int bpw = 8; > void *data = par; > u32 speed_hz; > int i, ret; > @@ -56,8 +57,6 @@ static int waveshare_command(struct mipi_dbi *mipi, u8 *cmd, u8 *par, > * The displays are Raspberry Pi HATs and connected to the 8-bit only > * SPI controller, so 16-bit command and parameters need byte swapping > * before being transferred as 8-bit on the big endian SPI bus. > - * Pixel data bytes have already been swapped before this function is > - * called. > */ > buf[0] = cpu_to_be16(*cmd); > gpiod_set_value_cansleep(mipi->dc, 0); > @@ -71,12 +70,18 @@ static int waveshare_command(struct mipi_dbi *mipi, u8 *cmd, u8 *par, > for (i = 0; i < num; i++) > buf[i] = cpu_to_be16(par[i]); > num *= 2; > - speed_hz = mipi_dbi_spi_cmd_max_speed(spi, num); > data = buf; > } > > + /* > + * Check whether pixel data bytes needs to be swapped or not > + */ > + if (*cmd == MIPI_DCS_WRITE_MEMORY_START && !mipi->swap_bytes) > + bpw = 16; > + > gpiod_set_value_cansleep(mipi->dc, 1); > - ret = mipi_dbi_spi_transfer(spi, speed_hz, 8, data, num); > + speed_hz = mipi_dbi_spi_cmd_max_speed(spi, num); > + ret = mipi_dbi_spi_transfer(spi, speed_hz, bpw, data, num); > free: > kfree(buf); > > Looks fine, but should somehow be tested on an RPi first to check if the 8bit fallback still works. Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
diff --git a/drivers/gpu/drm/tiny/ili9486.c b/drivers/gpu/drm/tiny/ili9486.c index bd37dfe8dd05..4d80a413338f 100644 --- a/drivers/gpu/drm/tiny/ili9486.c +++ b/drivers/gpu/drm/tiny/ili9486.c @@ -43,6 +43,7 @@ static int waveshare_command(struct mipi_dbi *mipi, u8 *cmd, u8 *par, size_t num) { struct spi_device *spi = mipi->spi; + unsigned int bpw = 8; void *data = par; u32 speed_hz; int i, ret; @@ -56,8 +57,6 @@ static int waveshare_command(struct mipi_dbi *mipi, u8 *cmd, u8 *par, * The displays are Raspberry Pi HATs and connected to the 8-bit only * SPI controller, so 16-bit command and parameters need byte swapping * before being transferred as 8-bit on the big endian SPI bus. - * Pixel data bytes have already been swapped before this function is - * called. */ buf[0] = cpu_to_be16(*cmd); gpiod_set_value_cansleep(mipi->dc, 0); @@ -71,12 +70,18 @@ static int waveshare_command(struct mipi_dbi *mipi, u8 *cmd, u8 *par, for (i = 0; i < num; i++) buf[i] = cpu_to_be16(par[i]); num *= 2; - speed_hz = mipi_dbi_spi_cmd_max_speed(spi, num); data = buf; } + /* + * Check whether pixel data bytes needs to be swapped or not + */ + if (*cmd == MIPI_DCS_WRITE_MEMORY_START && !mipi->swap_bytes) + bpw = 16; + gpiod_set_value_cansleep(mipi->dc, 1); - ret = mipi_dbi_spi_transfer(spi, speed_hz, 8, data, num); + speed_hz = mipi_dbi_spi_cmd_max_speed(spi, num); + ret = mipi_dbi_spi_transfer(spi, speed_hz, bpw, data, num); free: kfree(buf);
The pixel data for the ILI9486 is always 16-bits wide and it must be sent over the SPI bus. When the controller is only able to deal with 8-bit transfers, this 16-bits data needs to be swapped before the sending to account for the big endian bus, this is on the contrary not needed when the SPI controller already supports 16-bits transfers. The decision about swapping the pixel data or not is taken in the MIPI DBI code by probing the controller capabilities: if the controller only suppors 8-bit transfers the data is swapped, otherwise it is not. This swapping/non-swapping is relying on the assumption that when the controller does support 16-bit transactions then the data is sent unswapped in 16-bits-per-word over SPI. The problem with the ILI9486 driver is that it is forcing 8-bit transactions also for controllers supporting 16-bits, violating the assumption and corrupting the pixel data. Align the driver to what is done in the MIPI DBI code by adjusting the tranfer size to the maximum allowed by the SPI controller. Signed-off-by: Carlo Caione <ccaione@baylibre.com> --- drivers/gpu/drm/tiny/ili9486.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-)