[PATCH] drm/i915/bios: Move a variable assignment behind a null pointer check in intel_bios_encoder_supports_dp_dual_mode()

[PATCH] drm/i915/bios: Move a variable assignment behind a null pointer check in intel_bios_encoder_supports_dp_dual_mode()

[Markus Elfring]

From: Markus Elfring <elfring@users.sourceforge.net>
Date: Mon, 13 Jul 2026 15:56:46 +0200

The address of a data structure member was determined before
a corresponding null pointer check in the implementation of
the function “intel_bios_encoder_supports_dp_dual_mode”.

Thus avoid the risk for undefined behaviour by reducing the scope for
the variable “child” behind condition checks.

This issue was detected by using the Coccinelle software.

Fixes: 044cbc7a74c136f12a80c855cadd1b085084aef1 ("drm/i915/bios: Nuke DEVICE_TYPE_DP_DUAL_MODE_BITS")
Cc: stable@vger.kernel.org
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
---
 drivers/gpu/drm/i915/display/intel_bios.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
index 97cbae2e547e..1c4760373514 100644
--- a/drivers/gpu/drm/i915/display/intel_bios.c
+++ b/drivers/gpu/drm/i915/display/intel_bios.c
@@ -3514,8 +3514,6 @@ bool intel_bios_is_port_present(struct intel_display *display, enum port port)
 
 bool intel_bios_encoder_supports_dp_dual_mode(const struct intel_bios_encoder_data *devdata)
 {
-	const struct child_device_config *child = &devdata->child;
-
 	if (!devdata)
 		return false;
 
@@ -3523,6 +3521,8 @@ bool intel_bios_encoder_supports_dp_dual_mode(const struct intel_bios_encoder_da
 	    !intel_bios_encoder_supports_hdmi(devdata))
 		return false;
 
+	const struct child_device_config *child = &devdata->child;
+
 	if (dvo_port_type(child->dvo_port) == DVO_PORT_DPA)
 		return true;
 
-- 
2.55.0

Re: [PATCH] drm/i915/bios: Move a variable assignment behind a null pointer check in intel_bios_encoder_supports_dp_dual_mode()

[Rodrigo Vivi]

On Mon, Jul 13, 2026 at 04:05:53PM +0200, Markus Elfring wrote:
> From: Markus Elfring <elfring@users.sourceforge.net>
> Date: Mon, 13 Jul 2026 15:56:46 +0200
> 
> The address of a data structure member was determined before
> a corresponding null pointer check in the implementation of
> the function “intel_bios_encoder_supports_dp_dual_mode”.
> 
> Thus avoid the risk for undefined behaviour by reducing the scope for
> the variable “child” behind condition checks.
> 
> This issue was detected by using the Coccinelle software.
> 
> Fixes: 044cbc7a74c136f12a80c855cadd1b085084aef1 ("drm/i915/bios: Nuke DEVICE_TYPE_DP_DUAL_MODE_BITS")
> Cc: stable@vger.kernel.org
> Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
> ---
>  drivers/gpu/drm/i915/display/intel_bios.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index 97cbae2e547e..1c4760373514 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -3514,8 +3514,6 @@ bool intel_bios_is_port_present(struct intel_display *display, enum port port)
>  
>  bool intel_bios_encoder_supports_dp_dual_mode(const struct intel_bios_encoder_data *devdata)
>  {
> -	const struct child_device_config *child = &devdata->child;
> -
>  	if (!devdata)
>  		return false;
>  
> @@ -3523,6 +3521,8 @@ bool intel_bios_encoder_supports_dp_dual_mode(const struct intel_bios_encoder_da
>  	    !intel_bios_encoder_supports_hdmi(devdata))
>  		return false;
>  
> +	const struct child_device_config *child = &devdata->child;
> +

does it compile?

please keep the variable definition where it is and move only its
assignment after the null check.

Thanks,
Rodrigo.

>  	if (dvo_port_type(child->dvo_port) == DVO_PORT_DPA)
>  		return true;
>  
> -- 
> 2.55.0
> 

Re: [PATCH] drm/i915/bios: Move a variable assignment behind a null pointer check in intel_bios_encoder_supports_dp_dual_mode()

[Dan Carpenter]

On Tue, Jul 14, 2026 at 11:28:23AM -0400, Rodrigo Vivi wrote:
> On Mon, Jul 13, 2026 at 04:05:53PM +0200, Markus Elfring wrote:
> > From: Markus Elfring <elfring@users.sourceforge.net>
> > Date: Mon, 13 Jul 2026 15:56:46 +0200
> > 
> > The address of a data structure member was determined before
> > a corresponding null pointer check in the implementation of
> > the function “intel_bios_encoder_supports_dp_dual_mode”.
> > 
> > Thus avoid the risk for undefined behaviour by reducing the scope for
> > the variable “child” behind condition checks.
> > 
> > This issue was detected by using the Coccinelle software.
> > 
> > Fixes: 044cbc7a74c136f12a80c855cadd1b085084aef1 ("drm/i915/bios: Nuke DEVICE_TYPE_DP_DUAL_MODE_BITS")
> > Cc: stable@vger.kernel.org

Please stop adding Fixes tags to these and talking about "undefined
behavior" in the commit message.  Pointer math is defined...  It's
just a style preference on your part.

regards,
dan carpenter

Re: [PATCH] drm/i915/bios: Move a variable assignment behind a null pointer check in intel_bios_encoder_supports_dp_dual_mode()

[Markus Elfring]

>>> The address of a data structure member was determined before
>>> a corresponding null pointer check in the implementation of
>>> the function “intel_bios_encoder_supports_dp_dual_mode”.
>>>
>>> Thus avoid the risk for undefined behaviour by reducing the scope for
>>> the variable “child” behind condition checks.
>>>
>>> This issue was detected by using the Coccinelle software.
>>>
>>> Fixes: 044cbc7a74c136f12a80c855cadd1b085084aef1 ("drm/i915/bios: Nuke DEVICE_TYPE_DP_DUAL_MODE_BITS")
>>> Cc: stable@vger.kernel.org
> 
> Please stop adding Fixes tags to these and talking about "undefined
> behavior" in the commit message.  Pointer math is defined...

What does hinder you to take additional information sources better into account?


> It's just a style preference on your part.
Do you find the guidance appropriate according to the SEI CERT C Coding Standard?
https://cmu-sei.github.io/secure-coding-standards/sei-cert-c-coding-standard/rules/expressions-exp/exp34-c/

Regards,
Markus