[PATCH] drm/udl: make control msg static const.

[PATCH] drm/udl: make control msg static const.

[Dave Airlie]

From: Dave Airlie <airlied@redhat.com>

Thou shall not send control msg from the stack,
does that mean I can send it from the RO memory area?

Reported-by: poma
Signed-off-by: Dave Airlie <airlied@redhat.com>
---
 drivers/gpu/drm/udl/udl_main.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/udl/udl_main.c b/drivers/gpu/drm/udl/udl_main.c
index 29f0207..0798bcc 100644
--- a/drivers/gpu/drm/udl/udl_main.c
+++ b/drivers/gpu/drm/udl/udl_main.c
@@ -98,10 +98,10 @@ static int udl_parse_vendor_descriptor(struct drm_device *dev,
 static int udl_select_std_channel(struct udl_device *udl)
 {
 	int ret;
-	u8 set_def_chn[] = {0x57, 0xCD, 0xDC, 0xA7,
-			    0x1C, 0x88, 0x5E, 0x15,
-			    0x60, 0xFE, 0xC6, 0x97,
-			    0x16, 0x3D, 0x47, 0xF2};
+	static const u8 set_def_chn[] = {0x57, 0xCD, 0xDC, 0xA7,
+					 0x1C, 0x88, 0x5E, 0x15,
+					 0x60, 0xFE, 0xC6, 0x97,
+					 0x16, 0x3D, 0x47, 0xF2};
 
 	ret = usb_control_msg(udl->udev,
 			      usb_sndctrlpipe(udl->udev, 0),
-- 
2.5.5

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Re: [PATCH] drm/udl: make control msg static const.

[poma]

On 08.11.2016 07:39, Dave Airlie wrote:
> From: Dave Airlie <airlied@redhat.com>
> 
> Thou shall not send control msg from the stack,
> does that mean I can send it from the RO memory area?
> 
> Reported-by: poma
> Signed-off-by: Dave Airlie <airlied@redhat.com>
> ---
>  drivers/gpu/drm/udl/udl_main.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/udl/udl_main.c b/drivers/gpu/drm/udl/udl_main.c
> index 29f0207..0798bcc 100644
> --- a/drivers/gpu/drm/udl/udl_main.c
> +++ b/drivers/gpu/drm/udl/udl_main.c
> @@ -98,10 +98,10 @@ static int udl_parse_vendor_descriptor(struct drm_device *dev,
>  static int udl_select_std_channel(struct udl_device *udl)
>  {
>  	int ret;
> -	u8 set_def_chn[] = {0x57, 0xCD, 0xDC, 0xA7,
> -			    0x1C, 0x88, 0x5E, 0x15,
> -			    0x60, 0xFE, 0xC6, 0x97,
> -			    0x16, 0x3D, 0x47, 0xF2};
> +	static const u8 set_def_chn[] = {0x57, 0xCD, 0xDC, 0xA7,
> +					 0x1C, 0x88, 0x5E, 0x15,
> +					 0x60, 0xFE, 0xC6, 0x97,
> +					 0x16, 0x3D, 0x47, 0xF2};
>  
>  	ret = usb_control_msg(udl->udev,
>  			      usb_sndctrlpipe(udl->udev, 0),
> 


There is a compile time WARN:

$ make drivers/gpu/drm/udl/udl.ko
...
  CC [M]  drivers/gpu/drm/udl/udl_fb.o
drivers/gpu/drm/udl/udl_main.c: In function ‘udl_select_std_channel’:
drivers/gpu/drm/udl/udl_main.c:110:10: warning: passing argument 7 of ‘usb_control_msg’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
          set_def_chn, sizeof(set_def_chn),
          ^~~~~~~~~~~
In file included from drivers/gpu/drm/udl/udl_drv.h:17:0,
                 from drivers/gpu/drm/udl/udl_main.c:14:
./include/linux/usb.h:1685:12: note: expected ‘void *’ but argument is of type ‘const u8 * {aka const unsigned char *}’
 extern int usb_control_msg(struct usb_device *dev, unsigned int pipe,
            ^~~~~~~~~~~~~~~
  CC [M]  drivers/gpu/drm/udl/udl_transfer.o
  CC [M]  drivers/gpu/drm/udl/udl_gem.o
  CC [M]  drivers/gpu/drm/udl/udl_dmabuf.o
  LD [M]  drivers/gpu/drm/udl/udl.o
  MODPOST 1 modules
  CC      drivers/gpu/drm/udl/udl.mod.o
  LD [M]  drivers/gpu/drm/udl/udl.ko


Also there is a flood of waiting for request block:

$ dmesg | grep -P '(?=.*drm)(?=.*urb)'
[   72.482211] [drm] wait for urb interrupted: ffffffc2 available: 0
[   75.552227] [drm] wait for urb interrupted: ffffffc2 available: 0
[   76.576146] [drm] wait for urb interrupted: ffffffc2 available: 0
...
[  100.192153] [drm] wait for urb interrupted: ffffffc2 available: 0
[  101.216166] [drm] wait for urb interrupted: ffffffc2 available: 0
[  102.240141] [drm] wait for urb interrupted: ffffffc2 available: 0
...
[  200.416146] [drm] wait for urb interrupted: ffffffc2 available: 0
[  201.440208] [drm] wait for urb interrupted: ffffffc2 available: 0
[  204.384162] [drm] wait for urb interrupted: ffffffc2 available: 0
...
[  300.448151] [drm] wait for urb interrupted: ffffffc2 available: 0
[  301.920166] [drm] wait for urb interrupted: ffffffc2 available: 0
[  304.416147] [drm] wait for urb interrupted: ffffffc2 available: 0
...
[  370.016157] [drm] wait for urb interrupted: ffffffc2 available: 0
...


And finally,
Master Chef's special, the machine is KO'd due to trying out a module reload.



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