Read out and check the ID registers, so we can bail out if I2C
communication does not work or if the device is unknown. Tested on a
Renesas GrayHawk board (R-Car V4M) by using a wrong I2C address and by
not enabling RuntimePM for the device.
Signed-off-by: Wolfram Sang <wsa+rene...@sang-engineering.com>
---
Changes since v2:
* switched to a new approach suggested by Doug (Thanks!). We add a
dedicated read instead of using the first read. This prevents creating
the aux devices. As a side-gain, we check now if the chip at the address
is really the one we want to support.
drivers/gpu/drm/bridge/ti-sn65dsi86.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 87fffaa52bb0..8caa7918933d 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -36,6 +36,7 @@
#include <drm/drm_print.h>
#include <drm/drm_probe_helper.h>
+#define SN_DEVICE_ID_REGS 0x00 /* up to 0x07 */
#define SN_DEVICE_REV_REG 0x08
#define SN_DPPLL_SRC_REG 0x0A
#define DPPLL_CLK_SRC_DSICLK BIT(0)
@@ -1875,6 +1876,7 @@ static int ti_sn65dsi86_probe(struct i2c_client *client)
{
struct device *dev = &client->dev;
struct ti_sn65dsi86 *pdata;
+ u8 id_buf[8];
int ret;
if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
@@ -1918,6 +1920,16 @@ static int ti_sn65dsi86_probe(struct i2c_client *client)
if (ret)
return ret;
+ pm_runtime_get_sync(dev);
+ ret = regmap_bulk_read(pdata->regmap, SN_DEVICE_ID_REGS, id_buf,
ARRAY_SIZE(id_buf));
+ pm_runtime_put_autosuspend(dev);
+ if (ret)
+ return dev_err_probe(dev, ret, "failed to read device id\n");
+
+ /* The ID string is stored backwards */
+ if (strncmp(id_buf, "68ISD ", ARRAY_SIZE(id_buf)))
+ return dev_err_probe(dev, -EOPNOTSUPP, "unsupported device
id\n");
+
/*
* Break ourselves up into a collection of aux devices. The only real
* motiviation here is to solve the chicken-and-egg problem of probe
--
2.47.2
