drivers: led_strip: ws2812: Remove scratch selection

[thedjnK]

The WS2812 LED strip driver does not use a scratch byte, therefore free up a byte per pixel which was unused.

[simonguinot]

Thanks and well caught !

[fabiobaltieri]

@mbolivar-ampere ping

[simonguinot]

Hi @thedjnK,

After a second look I think this patch breaks the ws2812_gpio driver. See the ws2812_gpio_update_rgb fonction. Without the scratch byte and if the targeted color mapping is not RGB, then the red color (and possibly green too) is overwritten.

You can solve the issue by adding some intermediary variables. For example:

        /* Convert from RGB to on-wire format (e.g. GRB, GRBW, RGB, etc) */
        for (i = 0; i < num_pixels; i++) {
                uint8_t r = pixels[i].r;
                uint8_t g = pixels[i].g;
                uint8_t b = pixels[i].b;
                uint8_t j;

                for (j = 0; j < config->num_colors; j++) {
                        switch (config->color_mapping[j]) {
                        /* White channel is not supported by LED strip API. */
                        case LED_COLOR_ID_WHITE:
                                *ptr++ = 0;
                                break;
                        case LED_COLOR_ID_RED:
                                *ptr++ = r;
                                break;
                        case LED_COLOR_ID_GREEN:
                                *ptr++ = g;
                                break;
                        case LED_COLOR_ID_BLUE:
                                *ptr++ = b;
                                break;
                        default:
                                return -EINVAL;
                        }
                }
        }

Sorry for missing that with my initial review.

[simonguinot]

Sorry for missing that with my initial review.

And also for introducing this weakness with 4ada0bb

[simonguinot]

@thedjnK are you OK to update this PR ?

[thedjnK]

Yes, busy with other things but will get back to this some time

[simonguinot]

Thanks !