Hi Miquel,
On 6/9/23 16:59, Miquel Raynal wrote:
> A very basic debugging rule when a device is connected for the first
> time is to access a read-only register which contains known data in
> order to ensure the communication protocol is properly working. This
> driver lacked any read helper which is often a critical peace for
> fastening bring-ups.
I am afraid I don't get the last sentence. s/peace/piece? s/for
fastening/to speed up ? Only guessing here.
Best regards,
Michael
> Add a read helper and use it to verify the communication with the panel
> is working as soon as possible in order to fail early if this is not the
> case.
>
> Signed-off-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
> ---
> .../gpu/drm/panel/panel-sitronix-st7789v.c | 78 +++++++++++++++++++
> 1 file changed, 78 insertions(+)
>
> diff --git a/drivers/gpu/drm/panel/panel-sitronix-st7789v.c b/drivers/gpu/drm/panel/panel-sitronix-st7789v.c
> index 7de192a3a8aa..fb21d52a7a63 100644
> --- a/drivers/gpu/drm/panel/panel-sitronix-st7789v.c
> +++ b/drivers/gpu/drm/panel/panel-sitronix-st7789v.c
> @@ -113,6 +113,9 @@
> return val; \
> } while (0)
>
> +#define ST7789V_IDS { 0x85, 0x85, 0x52 }
> +#define ST7789V_IDS_SIZE 3
> +
> struct st7789v_panel_info {
> const struct drm_display_mode *display_mode;
> u16 width_mm;
> @@ -165,6 +168,77 @@ static int st7789v_write_data(struct st7789v *ctx, u8 cmd)
> return st7789v_spi_write(ctx, ST7789V_DATA, cmd);
> }
>
> +static int st7789v_read_data(struct st7789v *ctx, u8 cmd, u8 *buf,
> + unsigned int len)
> +{
> + struct spi_transfer xfer[2] = { };
> + struct spi_message msg;
> + u16 txbuf = ((ST7789V_COMMAND & 1) << 8) | cmd;
> + u16 rxbuf[4] = {};
> + u8 bit9 = 0;
> + int ret, i;
> +
> + switch (len) {
> + case 1:
> + case 3:
> + case 4:
> + break;
> + default:
> + return -EOPNOTSUPP;
> + }
> +
> + spi_message_init(&msg);
> +
> + xfer[0].tx_buf = &txbuf;
> + xfer[0].len = sizeof(txbuf);
> + spi_message_add_tail(&xfer[0], &msg);
> +
> + xfer[1].rx_buf = rxbuf;
> + xfer[1].len = len * 2;
> + spi_message_add_tail(&xfer[1], &msg);
> +
> + ret = spi_sync(ctx->spi, &msg);
> + if (ret)
> + return ret;
> +
> + for (i = 0; i < len; i++) {
> + buf[i] = rxbuf[i] >> i | (bit9 << (9 - i));
> + if (i)
> + bit9 = rxbuf[i] & GENMASK(i - 1, 0);
> + }
> +
> + return 0;
> +}
> +
> +static int st7789v_check_id(struct drm_panel *panel)
> +{
> + const u8 st7789v_ids[ST7789V_IDS_SIZE] = ST7789V_IDS;
> + struct st7789v *ctx = panel_to_st7789v(panel);
> + bool invalid_ids = false;
> + int ret, i;
> + u8 ids[3];
> +
> + ret = st7789v_read_data(ctx, MIPI_DCS_GET_DISPLAY_ID, ids, ST7789V_IDS_SIZE);
> + if (ret) {
> + dev_err(panel->dev, "Failed to read IDs\n");
> + return ret;
> + }
> +
> + for (i = 0; i < ST7789V_IDS_SIZE; i++) {
> + if (ids[i] != st7789v_ids[i]) {
> + invalid_ids = true;
> + break;
> + }
> + }
> +
> + if (invalid_ids) {
> + dev_err(panel->dev, "Unrecognized panel IDs");
> + return -EIO;
> + }
> +
> + return 0;
> +}
> +
> static const struct drm_display_mode default_mode = {
> .clock = 7000,
> .hdisplay = 240,
> @@ -237,6 +311,10 @@ static int st7789v_prepare(struct drm_panel *panel)
> gpiod_set_value(ctx->reset, 0);
> msleep(120);
>
> + ret = st7789v_check_id(panel);
> + if (ret)
> + return ret;
> +
> ST7789V_TEST(ret, st7789v_write_command(ctx, MIPI_DCS_EXIT_SLEEP_MODE));
>
> /* We need to wait 120ms after a sleep out command */
