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 <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 */
--
2.34.1
