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.
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 <[email protected]> --- .../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 */ -- 2.34.1
