[PATCH] drm/bridge: waveshare-dsi: Fix signedness bug

[PATCH] drm/bridge: waveshare-dsi: Fix signedness bug

[Ethan Tidmore]

The function drm_of_get_data_lanes_count_ep() returns negative error
codes and dsi->lanes is an unsigned integer, so the check (dsi->lanes <
0) is always impossible.

Make the return value of drm_of_get_data_lanes_count_ep() be assigned to
ret, check for error, and then assign dsi->lanes to ret.

Detected by Smatch:
drivers/gpu/drm/bridge/waveshare-dsi.c:70 ws_bridge_attach_dsi() warn:
unsigned 'dsi->lanes' is never less than zero.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202603060341.hNj0pl9L-lkp@intel.com/
Fixes: fca11428425e9 ("drm/bridge: waveshare-dsi: Add support for 1..4 DSI data lanes")
Signed-off-by: Ethan Tidmore <ethantidmore06@gmail.com>
---
 drivers/gpu/drm/bridge/waveshare-dsi.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/bridge/waveshare-dsi.c b/drivers/gpu/drm/bridge/waveshare-dsi.c
index 0497c7ecbc7a..32d40414adb9 100644
--- a/drivers/gpu/drm/bridge/waveshare-dsi.c
+++ b/drivers/gpu/drm/bridge/waveshare-dsi.c
@@ -66,11 +66,13 @@ static int ws_bridge_attach_dsi(struct ws_bridge *ws)
 	dsi->mode_flags = MIPI_DSI_MODE_VIDEO_HSE | MIPI_DSI_MODE_VIDEO |
 			  MIPI_DSI_CLOCK_NON_CONTINUOUS;
 	dsi->format = MIPI_DSI_FMT_RGB888;
-	dsi->lanes = drm_of_get_data_lanes_count_ep(dev->of_node, 0, 0, 1, 4);
-	if (dsi->lanes < 0) {
+	ret = drm_of_get_data_lanes_count_ep(dev->of_node, 0, 0, 1, 4);
+	if (ret < 0) {
 		dev_warn(dev, "Invalid or missing DSI lane count %d, falling back to 2 lanes\n",
-			 dsi->lanes);
+			 ret);
 		dsi->lanes = 2;	/* Old DT backward compatibility */
+	} else {
+		dsi->lanes = ret;
 	}
 
 	ret = devm_mipi_dsi_attach(dev, dsi);
-- 
2.53.0

Re: [PATCH] drm/bridge: waveshare-dsi: Fix signedness bug

[Marek Vasut]

On 3/7/26 4:32 AM, Ethan Tidmore wrote:
> The function drm_of_get_data_lanes_count_ep() returns negative error
> codes and dsi->lanes is an unsigned integer, so the check (dsi->lanes <
> 0) is always impossible.
> 
> Make the return value of drm_of_get_data_lanes_count_ep() be assigned to
> ret, check for error, and then assign dsi->lanes to ret.
> 
> Detected by Smatch:
> drivers/gpu/drm/bridge/waveshare-dsi.c:70 ws_bridge_attach_dsi() warn:
> unsigned 'dsi->lanes' is never less than zero.
I already sent:

[PATCH] drm/bridge: waveshare-dsi: Use temporary signed variable for DSI 
lanes validation

Re: [PATCH] drm/bridge: waveshare-dsi: Fix signedness bug

[Ethan Tidmore]

On Fri Mar 6, 2026 at 9:44 PM CST, Marek Vasut wrote:
> On 3/7/26 4:32 AM, Ethan Tidmore wrote:

> I already sent:
>
> [PATCH] drm/bridge: waveshare-dsi: Use temporary signed variable for DSI 
> lanes validation

Sorry about that! I glanced at lore looking for the kernel test robot,
should have looked for patches already for this.

Thanks,

ET

Re: [PATCH] drm/bridge: waveshare-dsi: Fix signedness bug

[Marek Vasut]

On 3/7/26 7:42 AM, Ethan Tidmore wrote:
> On Fri Mar 6, 2026 at 9:44 PM CST, Marek Vasut wrote:
>> On 3/7/26 4:32 AM, Ethan Tidmore wrote:
> 
>> I already sent:
>>
>> [PATCH] drm/bridge: waveshare-dsi: Use temporary signed variable for DSI
>> lanes validation
> 
> Sorry about that! I glanced at lore looking for the kernel test robot,
> should have looked for patches already for this.
Actually, looking at it one more time, the patch I sent is missing the 
update of dev_warn() , so this patch is the better fix:

Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>

Thank you !

Re: [PATCH] drm/bridge: waveshare-dsi: Fix signedness bug

[Luca Ceresoli]

On Sat Mar 7, 2026 at 4:32 AM CET, Ethan Tidmore wrote:
> The function drm_of_get_data_lanes_count_ep() returns negative error
> codes and dsi->lanes is an unsigned integer, so the check (dsi->lanes <
> 0) is always impossible.
>
> Make the return value of drm_of_get_data_lanes_count_ep() be assigned to
> ret, check for error, and then assign dsi->lanes to ret.
>
> Detected by Smatch:
> drivers/gpu/drm/bridge/waveshare-dsi.c:70 ws_bridge_attach_dsi() warn:
> unsigned 'dsi->lanes' is never less than zero.
>
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202603060341.hNj0pl9L-lkp@intel.com/
> Fixes: fca11428425e9 ("drm/bridge: waveshare-dsi: Add support for 1..4 DSI data lanes")
> Signed-off-by: Ethan Tidmore <ethantidmore06@gmail.com>

Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

Re: [PATCH] drm/bridge: waveshare-dsi: Fix signedness bug

[Marek Vasut]

On 3/9/26 12:10 PM, Luca Ceresoli wrote:
> On Sat Mar 7, 2026 at 4:32 AM CET, Ethan Tidmore wrote:
>> The function drm_of_get_data_lanes_count_ep() returns negative error
>> codes and dsi->lanes is an unsigned integer, so the check (dsi->lanes <
>> 0) is always impossible.
>>
>> Make the return value of drm_of_get_data_lanes_count_ep() be assigned to
>> ret, check for error, and then assign dsi->lanes to ret.
>>
>> Detected by Smatch:
>> drivers/gpu/drm/bridge/waveshare-dsi.c:70 ws_bridge_attach_dsi() warn:
>> unsigned 'dsi->lanes' is never less than zero.
>>
>> Reported-by: kernel test robot <lkp@intel.com>
>> Closes: https://lore.kernel.org/oe-kbuild-all/202603060341.hNj0pl9L-lkp@intel.com/
>> Fixes: fca11428425e9 ("drm/bridge: waveshare-dsi: Add support for 1..4 DSI data lanes")
>> Signed-off-by: Ethan Tidmore <ethantidmore06@gmail.com>
> 
> Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>

(it seems FDO patchwork did not pick this up)

Re: [PATCH] drm/bridge: waveshare-dsi: Fix signedness bug

[Luca Ceresoli]

On Fri, 06 Mar 2026 21:32:45 -0600, Ethan Tidmore wrote:
> The function drm_of_get_data_lanes_count_ep() returns negative error
> codes and dsi->lanes is an unsigned integer, so the check (dsi->lanes <
> 0) is always impossible.
> 
> Make the return value of drm_of_get_data_lanes_count_ep() be assigned to
> ret, check for error, and then assign dsi->lanes to ret.
> 
> [...]

Applied, thanks!

[1/1] drm/bridge: waveshare-dsi: Fix signedness bug
      commit: a469749640fbcd2f49ab05fb83cca3da07f35ee3

Best regards,
-- 
Luca Ceresoli <luca.ceresoli@bootlin.com>