[U-Boot] [PATCH v2 10/22] spi: Add error checking for invalid bus widths

[Fabio Estevam]

On Sat, Nov 19, 2016 at 6:04 PM, Simon Glass <sjg at chromium.org> wrote:

>> EPROTONOSUPPORT means: /* Protocol not supported */, which does not
>> seem to be very appropriate here.
>
> This is a protocol as far as I can see - you can either use one pin or
> four pins.

Actually they are SPI modes: one, two or four pins.

>> Why not return -EINVAL instead?
>
> The value is valid but is not supported. If we just return -EINVAL for
> anything we don't like, it makes it harder to root-cause the error. In
> particular we use -EINVAL when decoding the device tree. But
> EPROTONOSUPPORT is not widely used.

I think the current behaviour of not returning an error code on an
invalid mode is correct and it matches what the kernel does in
drivers/spi/spi.c.

If an invalid mode is passed we just ignore it and operate in single
mode instead.

Maybe we can make this clearer by printing a message like this:

--- a/drivers/spi/spi-uclass.c
+++ b/drivers/spi/spi-uclass.c
@@ -408,7 +408,7 @@ int spi_slave_ofdata_to_platdata(const void *blob, int node,
                mode |= SPI_TX_QUAD;
                break;
        default:
-               error("spi-tx-bus-width %d not supported\n", value);
+               printf("spi-tx-bus-width %d not supported, operating
in single mode\n", value);
                break;
        }

@@ -423,7 +423,7 @@ int spi_slave_ofdata_to_platdata(const void *blob, int node,
                mode |= SPI_RX_QUAD;
                break;
        default:
-               error("spi-rx-bus-width %d not supported\n", value);
+               printf("spi-rx-bus-width %d not supported, operating
in single mode\n", value);
                break;
        }