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Data writes for the ssd130x 4-wire SPI protocol need special handling, due
the Data/Command control (D/C) pin having to be toggled prior to the write.
The regmap API only allowed drivers to provide .reg_{read,write} callbacks
to do per register read/write, but didn't provide a way for drivers to do
the same for bulk read/writes.
For this reason, a custom regmap bus was used by the driver just to define
a bulk write callback that implements the D/C pin toggling. But the regmap
API has been extended to support defining bulk read/write handlers, so the
custom regmap bus is not needed anymore and could just be dropped.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220618174338.2253021-1-javierm@redhat.com
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The kernel test robot reports a compile warning due the ssd130x_spi_table
variable being defined but not used. This happen when ssd130x-spi driver
is built-in instead of being built as a module, i.e:
CC drivers/gpu/drm/solomon/ssd130x-spi.o
AR drivers/base/firmware_loader/built-in.a
AR drivers/base/built-in.a
CC kernel/trace/trace.o
drivers/gpu/drm/solomon/ssd130x-spi.c:155:35: warning: ‘ssd130x_spi_table’ defined but not used [-Wunused-const-variable=]
155 | static const struct spi_device_id ssd130x_spi_table[] = {
| ^~~~~~~~~~~~~~~~~
The driver shouldn't need a SPI device ID table and only have an OF device
ID table, but the former is needed to workaround an issue in the SPI core.
This always reports a MODALIAS of the form "spi:<device>" even for devices
registered through Device Trees.
But the table is only needed when the driver built as a module to populate
the .ko alias info. It's not needed when the driver is built-in the kernel.
Fixes: 74373977d2ca ("drm/solomon: Add SSD130x OLED displays SPI support")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220530140246.742469-1-javierm@redhat.com
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The ssd130x driver only provides the core support for these devices but it
does not have any bus transport logic. Add a driver to interface over SPI.
There is a difference in the communication protocol when using 4-wire SPI
instead of I2C. For the latter, a control byte that contains a D/C# field
has to be sent. This field tells the controller whether the data has to be
written to the command register or to the graphics display data memory.
But for 4-wire SPI that control byte is not used, instead a real D/C# line
must be pulled HIGH for commands data and LOW for graphics display data.
For this reason the standard SPI regmap can't be used and a custom .write
bus handler is needed.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patchwork.freedesktop.org/patch/msgid/20220419214824.335075-6-javierm@redhat.com
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