Re: [PATCH v6 2/3] drm/ch1115: add support for Chipwealth CH1115 OLED controller

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] drm/ch1115: out-of-range display offset 64 sent in ch1115_oled_init()
- [Medium] drm/ch1115: missing DC-DC disable in ch1115_encoder_atomic_disable()
--

commit e5268b4f2a7c534421925bdee0145caf63c50632
Author: Nicolás Antinori <nico.antinori.7@gmail.com>

drm/ch1115: add support for Chipwealth CH1115 OLED controller

This commit adds a DRM driver for Chipwealth CH1115 monochrome dot matrix
OLED panels connected over I2C.

> diff --git a/drivers/gpu/drm/tiny/ch1115-i2c.c b/drivers/gpu/drm/tiny/ch1115-i2c.c
> new file mode 100644
> index 0000000000000..08fee5a09f4f9
> --- /dev/null
> +++ b/drivers/gpu/drm/tiny/ch1115-i2c.c
> @@ -0,0 +1,859 @@

[ ... ]

> +static int ch1115_oled_init(struct ch1115_device *ch1115)
> +{
> +	u8 commands[] = {
> +		CH1115_CMD_OFF,
> +
> +		CH1115_CMD_CLOCK_DIVIDE_RATIO,
> +		CH1115_VAL_CLOCK_DIVIDE_RATIO(CH1115_VAL_CLOCK_OSC_FREQ,
> +					      CH1115_VAL_CLOCK_DIV_RATIO),
> +
> +		CH1115_CMD_MUX_RATIO,
> +		ch1115->height - 1,
> +
> +		CH1115_CMD_OFFSET,
> +		ch1115->flip_vertical
> +			? ch1115->y_start_offset
> +			: CH1115_MAX_HEIGHT - ch1115->y_start_offset,

[Severity: Medium]
Does ch1115_oled_init() send an out-of-range value for CH1115_CMD_OFFSET when
flip_vertical is false and y_start_offset is 0?

In ch1115_parse_dt(), y_start_offset defaults to 0 when the chipwealth,offset
property is omitted, and is otherwise restricted to [0, CH1115_MAX_HEIGHT - 1]
(0 to 63):

	ret = of_property_read_u32(np, "chipwealth,offset", &val);
	if (ret) {
		ch1115->y_start_offset = 0;
	} else {
		if (val > CH1115_MAX_HEIGHT - 1) {
			dev_err(dev, "chipwealth,offset=%d must be [0-%d]\n",
				val, CH1115_MAX_HEIGHT - 1);
			return -EINVAL;
		}
		ch1115->y_start_offset = (u8)val;
	}

When ch1115_encoder_atomic_enable() calls ch1115_oled_init() with
flip_vertical set to false and y_start_offset set to 0, the expression
CH1115_MAX_HEIGHT - ch1115->y_start_offset evaluates to 64 (0x40), which
overflows the 6-bit [0, 63] vertical offset field instead of wrapping modulo
CH1115_MAX_HEIGHT to 0.

[ ... ]

> +static void ch1115_encoder_atomic_enable(struct drm_encoder *encoder,
> +					 struct drm_atomic_commit *state)
> +{
> +	struct drm_device *drm = encoder->dev;
> +	struct ch1115_device *ch1115 = drm_to_ch1115(drm);
> +	int ret;
> +
> +	ret = ch1115_oled_init(ch1115);
> +	if (ret < 0)
> +		return;
> +
> +	u8 command = CH1115_CMD_ON;
> +
> +	ret = ch1115_send_command_list(ch1115, &command, 1);
> +	if (ret < 0)
> +		return;
> +
> +	backlight_enable(ch1115->bl_dev);
> +}
> +
> +static void ch1115_encoder_atomic_disable(struct drm_encoder *encoder,
> +					  struct drm_atomic_commit *state)
> +{
> +	struct drm_device *drm = encoder->dev;
> +	struct ch1115_device *ch1115 = drm_to_ch1115(drm);
> +
> +	backlight_disable(ch1115->bl_dev);
> +
> +	u8 command = CH1115_CMD_OFF;
> +
> +	ch1115_send_command_list(ch1115, &command, 1);
> +}

[Severity: Medium]
Should ch1115_encoder_atomic_disable() also disable the internal DC-DC
converter?

When the encoder is enabled, ch1115_encoder_atomic_enable() calls
ch1115_oled_init(), which turns on the DC-DC converter with CH1115_CMD_DC_DC
and CH1115_VAL_DC_DC_ON. However, when the display is disabled via KMS or
during system shutdown via ch1115_shutdown() -> drm_atomic_helper_shutdown(),
ch1115_encoder_atomic_disable() only sends CH1115_CMD_OFF, leaving the DC-DC
converter enabled.

By contrast, ch1115_remove() explicitly sends CH1115_CMD_OFF,
CH1115_CMD_DC_DC, and CH1115_VAL_DC_DC_OFF after calling
drm_atomic_helper_shutdown():

	u8 cmd_list[] = {
		CH1115_CMD_OFF,
		CH1115_CMD_DC_DC,
		CH1115_VAL_DC_DC_OFF,
	};

	drm_dev_unplug(&ch1115->dev);
	drm_atomic_helper_shutdown(&ch1115->dev);

	ch1115_send_command_list(ch1115, cmd_list, ARRAY_SIZE(cmd_list));

If ch1115_encoder_atomic_disable() sent CH1115_CMD_OFF, CH1115_CMD_DC_DC, and
CH1115_VAL_DC_DC_OFF, wouldn't that properly power down the DC-DC converter on
both KMS disable and ch1115_shutdown(), while avoiding the duplicate command
sequence in ch1115_remove()?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1793735996.git.nico.antinori.7@gmail.com?part=2