| Message ID | 20171006195826.27500-1-robert.jarzmik@free.fr (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 06/10/17 20:58, Robert Jarzmik wrote: > Currently the LCD display (TD035S) on the cm-x300 platform is broken and > remains blank. > > The TD0245S specification requires that the chipselect is toggled > between commands sent to the panel. This was also the purpose of the > former patch of commit f64dcac0b124 ("backlight: tdo24m: ensure chip > select changes between transfers"). > > Unfortunately, the "cs_change" field of a SPI transfer is > misleading. Its true meaning is that for a SPI message holding multiple > transfers, the chip select is toggled between each transfer, but for the > last transfer it remains asserted. > > In this driver, all the SPI messages contain exactly one transfer, which > means that each transfer is the last of its message, and as a > consequence the chip select is never toggled. > > This fix makes the TD035S work again on a cm-x300 board. > > Fixes: f64dcac0b124 ("backlight: tdo24m: ensure chip select changes > between transfers") > Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr> I'm a tiny bit worried about see-saw bug fixing here but nevertheless this change looks correct to me. Mike's change was eight years ago and it is reasonable to hope that the patch was really just working around a (hopefully long fixed) bug in the SPI driver! Acked-by: Daniel Thompson <daniel.thompson@linaro.org> > --- > drivers/video/backlight/tdo24m.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/video/backlight/tdo24m.c b/drivers/video/backlight/tdo24m.c > index eab1f842f9c0..e4bd63e9db6b 100644 > --- a/drivers/video/backlight/tdo24m.c > +++ b/drivers/video/backlight/tdo24m.c > @@ -369,7 +369,7 @@ static int tdo24m_probe(struct spi_device *spi) > > spi_message_init(m); > > - x->cs_change = 1; > + x->cs_change = 0; > x->tx_buf = &lcd->buf[0]; > spi_message_add_tail(x, m); > > -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Daniel Thompson <daniel.thompson@linaro.org> writes: > On 06/10/17 20:58, Robert Jarzmik wrote: > > I'm a tiny bit worried about see-saw bug fixing here but nevertheless this > change looks correct to me. > > Mike's change was eight years ago and it is reasonable to hope that the patch > was really just working around a (hopefully long fixed) bug in the SPI driver! Actually I think it's the case. And the driver bug fix is here : a52db659c79c ("spi: pxa2xx: Fix cs_change management") And please don't apply this as there are 2 other LCDs which are affected by the same issue and reported by Andrea, for which I had not correlated the issue until yesterday, so I'll have to respin this 2 others files, namely : - drivers/video/backlight/corgi_lcd.c. - drivers/video/backlight/tosa_lcd.c. There 2 other candidates I won't touch as they are not under my maintainance, and I have no way to test them : - ili922x.c - ltv350qv.c > Acked-by: Daniel Thompson <daniel.thompson@linaro.org> Thanks, but there will be a v2 with exactly the same fix in 3 files. Cheers. -- Robert -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/video/backlight/tdo24m.c b/drivers/video/backlight/tdo24m.c index eab1f842f9c0..e4bd63e9db6b 100644 --- a/drivers/video/backlight/tdo24m.c +++ b/drivers/video/backlight/tdo24m.c @@ -369,7 +369,7 @@ static int tdo24m_probe(struct spi_device *spi) spi_message_init(m); - x->cs_change = 1; + x->cs_change = 0; x->tx_buf = &lcd->buf[0]; spi_message_add_tail(x, m);
Currently the LCD display (TD035S) on the cm-x300 platform is broken and remains blank. The TD0245S specification requires that the chipselect is toggled between commands sent to the panel. This was also the purpose of the former patch of commit f64dcac0b124 ("backlight: tdo24m: ensure chip select changes between transfers"). Unfortunately, the "cs_change" field of a SPI transfer is misleading. Its true meaning is that for a SPI message holding multiple transfers, the chip select is toggled between each transfer, but for the last transfer it remains asserted. In this driver, all the SPI messages contain exactly one transfer, which means that each transfer is the last of its message, and as a consequence the chip select is never toggled. This fix makes the TD035S work again on a cm-x300 board. Fixes: f64dcac0b124 ("backlight: tdo24m: ensure chip select changes between transfers") Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr> --- drivers/video/backlight/tdo24m.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)