Hi Stephen,
On 10/07/2016 08:33 PM, Stephen Warren wrote:
> On 10/07/2016 07:25 AM, Ralf Ramsauer wrote:
>> Hi,
>>
>> I'm running a Jetson TK1 on mainline Linux. To enable userspace SPI, I
>> modified the device-tree by:
>>
>> /* Expansion TS_SPI_* */
>> spi@7000d400 {
>> status = "okay";
>> + spidev@0 {
>> + compatible = "spidev";
>> + reg = <0>;
>> + spi-max-frequency = <25000000>;
>> + };
>> };
>>
>> This works fine. Is it possible to use arbitrary GPIOs as additional
>> chip-selects?
>>
>> What would I have to do If I'd like to add PU0 or PU1 (sysfs
>> gpio160/161) as chip-selects?
>
> According to Documentation/devicetree/bindings/spi/spi-bus.txt, there
> are standard properties you can use for GPIO chip-select signals, and it
> looks like the SPI core code handles this itself. However, judging by a
Yes, I already followed those instructions and it didn't work. Other CSs
seem to be ignored, without any warnings while the native CS line still
keeps working. That's why I came up with this post. Adding a line to the
DT like
cs-gpios = <0>, <&gpio TEGRA_GPIO(X, Y) GPIO_ACTIVE_LOW>;
should actually (at least syntactically and semantically) be fine for an
additional CS, right?
> quick look at the Tegra SPI driver, it doesn't fully support that since
> it always attempts to program the HW chip-selects. If you make the HW CS
> logic in the driver conditional, and add the DT properties mentioned in
> spi-bus.txt, it should work.
Oh no, doesn't sound good. Actually I didn't want to touch driver
code... Well, I'll have a look into other drivers that already support
it and compare it to the tegra driver.
Ralf
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