[PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present

[PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present

[Javier Martinez Canillas]

On coreboot platforms, a system framebuffer may be provided to the Linux
kernel by filling a LB_TAG_FRAMEBUFFER entry in the coreboot table. But
a coreboot payload (e.g: SeaBIOS) could also provide its own framebuffer
information to the Linux kernel.

If that's the case, arch x86 boot code will fill the global screen_info
data and this used by the Generic System Framebuffers (sysfb) framework,
to register a platform device with pdata about the system's framebuffer.

But later, the framebuffer_coreboot driver will try to do the same and
attempt to register a "simple-framebuffer" platform device (using the
information from the coreboot table), which will lead to an error due a
device with the same name already being registered:

    sysfs: cannot create duplicate filename '/bus/platform/devices/simple-framebuffer.0'
    ...
    coreboot: could not register framebuffer
    framebuffer coreboot8: probe with driver framebuffer failed with error -17

To prevent this issue, make the framebuffer_core driver to not register
a platform device if the global struct screen_info data has been filled.

Reported-by: Brian Norris <briannorris@chromium.org>
Closes: https://lore.kernel.org/all/ZuCG-DggNThuF4pj@b20ea791c01f/T/#ma7fb65acbc1a56042258adac910992bb225a20d2
Suggested-by: Julius Werner <jwerner@chromium.org>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
---

Changes in v3:
- Fix coreboot spelling to be all in lowercase (Julius Werner).

Changes in v2:
- Declare the struct screen_info as constant variable (Thomas Zimmermann).
- Use screen_info_video_type() instead of checking the screen_info video
  types directly (Thomas Zimmermann).
- Fix missing "device" word in a comment (Brian Norris).
- Fix some mispellings in a comment (Brian Norris).
- Change error code returned from -EINVAL to -ENODEV (Brian Norris).

 drivers/firmware/google/framebuffer-coreboot.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/firmware/google/framebuffer-coreboot.c b/drivers/firmware/google/framebuffer-coreboot.c
index daadd71d8ddd..f722292e7684 100644
--- a/drivers/firmware/google/framebuffer-coreboot.c
+++ b/drivers/firmware/google/framebuffer-coreboot.c
@@ -15,6 +15,7 @@
 #include <linux/module.h>
 #include <linux/platform_data/simplefb.h>
 #include <linux/platform_device.h>
+#include <linux/screen_info.h>
 
 #include "coreboot_table.h"
 
@@ -27,8 +28,10 @@ static int framebuffer_probe(struct coreboot_device *dev)
 	int i;
 	u32 length;
 	struct lb_framebuffer *fb = &dev->framebuffer;
+	const struct screen_info *si = &screen_info;
 	struct platform_device *pdev;
 	struct resource res;
+	unsigned int type;
 	struct simplefb_platform_data pdata = {
 		.width = fb->x_resolution,
 		.height = fb->y_resolution,
@@ -36,6 +39,20 @@ static int framebuffer_probe(struct coreboot_device *dev)
 		.format = NULL,
 	};
 
+	/*
+	 * On coreboot systems, the advertised LB_TAG_FRAMEBUFFER entry
+	 * in the coreboot table should only be used if the payload did
+	 * not pass a framebuffer information to the Linux kernel.
+	 *
+	 * If the global screen_info data has been filled, the Generic
+	 * System Framebuffers (sysfb) will already register a platform
+	 * device and pass that screen_info as platform_data to a driver
+	 * that can scan-out using the system provided framebuffer.
+	 */
+	type = screen_info_video_type(si);
+	if (type)
+		return -ENODEV;
+
 	if (!fb->physical_address)
 		return -ENODEV;
 
-- 
2.46.0

Re: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present

[kernel test robot]

Hi Javier,

kernel test robot noticed the following build errors:

[auto build test ERROR on chrome-platform/for-next]
[also build test ERROR on chrome-platform/for-firmware-next linus/master v6.11-rc7 next-20240913]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Javier-Martinez-Canillas/firmware-coreboot-Don-t-register-a-pdev-if-screen_info-data-is-present/20240914-053323
base:   https://git.kernel.org/pub/scm/linux/kernel/git/chrome-platform/linux.git for-next
patch link:    https://lore.kernel.org/r/20240913213246.1549213-1-javierm%40redhat.com
patch subject: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present
config: csky-randconfig-002-20240915 (https://download.01.org/0day-ci/archive/20240915/202409150915.n7egvNYa-lkp@intel.com/config)
compiler: csky-linux-gcc (GCC) 14.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240915/202409150915.n7egvNYa-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202409150915.n7egvNYa-lkp@intel.com/

All errors (new ones prefixed by >>, old ones prefixed by <<):

WARNING: modpost: missing MODULE_DESCRIPTION() in kernel/locking/test-ww_mutex.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/usb/serial/usb_debug.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/usb/serial/mxuport.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/usb/serial/symbolserial.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/devfreq/governor_simpleondemand.o
>> ERROR: modpost: "screen_info" [drivers/firmware/google/framebuffer-coreboot.ko] undefined!

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present

[kernel test robot]

Hi Javier,

kernel test robot noticed the following build errors:

[auto build test ERROR on chrome-platform/for-next]
[also build test ERROR on chrome-platform/for-firmware-next linus/master v6.11-rc7 next-20240913]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Javier-Martinez-Canillas/firmware-coreboot-Don-t-register-a-pdev-if-screen_info-data-is-present/20240914-053323
base:   https://git.kernel.org/pub/scm/linux/kernel/git/chrome-platform/linux.git for-next
patch link:    https://lore.kernel.org/r/20240913213246.1549213-1-javierm%40redhat.com
patch subject: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present
config: riscv-randconfig-001-20240915 (https://download.01.org/0day-ci/archive/20240915/202409151528.CIWZRPBq-lkp@intel.com/config)
compiler: clang version 15.0.7 (https://github.com/llvm/llvm-project 8dfdcc7b7bf66834a761bd8de445840ef68e4d1a)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240915/202409151528.CIWZRPBq-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202409151528.CIWZRPBq-lkp@intel.com/

All errors (new ones prefixed by >>):

>> ld.lld: error: undefined symbol: screen_info
   >>> referenced by framebuffer-coreboot.c:27 (drivers/firmware/google/framebuffer-coreboot.c:27)
   >>>               drivers/firmware/google/framebuffer-coreboot.o:(framebuffer_probe) in archive vmlinux.a
   >>> referenced by framebuffer-coreboot.c:27 (drivers/firmware/google/framebuffer-coreboot.c:27)
   >>>               drivers/firmware/google/framebuffer-coreboot.o:(framebuffer_probe) in archive vmlinux.a

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present

[Tzung-Bi Shih]

On Fri, Sep 13, 2024 at 11:32:29PM +0200, Javier Martinez Canillas wrote:
> @@ -27,8 +28,10 @@ static int framebuffer_probe(struct coreboot_device *dev)
>  	int i;
>  	u32 length;
>  	struct lb_framebuffer *fb = &dev->framebuffer;
> +	const struct screen_info *si = &screen_info;
>  	struct platform_device *pdev;
>  	struct resource res;
> +	unsigned int type;
>  	struct simplefb_platform_data pdata = {
>  		.width = fb->x_resolution,
>  		.height = fb->y_resolution,
> @@ -36,6 +39,20 @@ static int framebuffer_probe(struct coreboot_device *dev)
>  		.format = NULL,
>  	};
>  
> +	/*
> +	 * On coreboot systems, the advertised LB_TAG_FRAMEBUFFER entry
> +	 * in the coreboot table should only be used if the payload did
> +	 * not pass a framebuffer information to the Linux kernel.
> +	 *
> +	 * If the global screen_info data has been filled, the Generic
> +	 * System Framebuffers (sysfb) will already register a platform
> +	 * device and pass that screen_info as platform_data to a driver
> +	 * that can scan-out using the system provided framebuffer.
> +	 */
> +	type = screen_info_video_type(si);
> +	if (type)
> +		return -ENODEV;

Given that `type` and `si` aren't used in otherwhere, the local variables can
be dropped.

I haven't had chance to see how to fix the 0-day build errors properly.  If you
have chance to send the next versions, please drop the local variables.

Re: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present

[Thomas Zimmermann]

Hi

Am 15.09.24 um 09:44 schrieb kernel test robot:
> Hi Javier,
>
> kernel test robot noticed the following build errors:
>
> [auto build test ERROR on chrome-platform/for-next]
> [also build test ERROR on chrome-platform/for-firmware-next linus/master v6.11-rc7 next-20240913]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Javier-Martinez-Canillas/firmware-coreboot-Don-t-register-a-pdev-if-screen_info-data-is-present/20240914-053323
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/chrome-platform/linux.git for-next
> patch link:    https://lore.kernel.org/r/20240913213246.1549213-1-javierm%40redhat.com
> patch subject: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present
> config: riscv-randconfig-001-20240915 (https://download.01.org/0day-ci/archive/20240915/202409151528.CIWZRPBq-lkp@intel.com/config)
> compiler: clang version 15.0.7 (https://github.com/llvm/llvm-project 8dfdcc7b7bf66834a761bd8de445840ef68e4d1a)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240915/202409151528.CIWZRPBq-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202409151528.CIWZRPBq-lkp@intel.com/
>
> All errors (new ones prefixed by >>):
>
>>> ld.lld: error: undefined symbol: screen_info
>     >>> referenced by framebuffer-coreboot.c:27 (drivers/firmware/google/framebuffer-coreboot.c:27)
>     >>>               drivers/firmware/google/framebuffer-coreboot.o:(framebuffer_probe) in archive vmlinux.a
>     >>> referenced by framebuffer-coreboot.c:27 (drivers/firmware/google/framebuffer-coreboot.c:27)
>     >>>               drivers/firmware/google/framebuffer-coreboot.o:(framebuffer_probe) in archive vmlinux.a

Not all platforms define screen_info. Maybe fix this by following 
Tzung-Bi's advice of removing the local variables and then guard the 
test by CONFIG_SYSFB. If SYSFB has been defined, screen_info has to be 
there. It's not a super pretty solution, though.

Best regards
Thomas

>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

Re: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present

[Javier Martinez Canillas]

Thomas Zimmermann <tzimmermann@suse.de> writes:

Hello Thomas and Tzung-Bi,

> Hi
>
> Am 15.09.24 um 09:44 schrieb kernel test robot:
>> Hi Javier,
>>
>> kernel test robot noticed the following build errors:
>>
>> [auto build test ERROR on chrome-platform/for-next]
>> [also build test ERROR on chrome-platform/for-firmware-next linus/master v6.11-rc7 next-20240913]
>> [If your patch is applied to the wrong git tree, kindly drop us a note.
>> And when submitting patch, we suggest to use '--base' as documented in
>> https://git-scm.com/docs/git-format-patch#_base_tree_information]
>>
>> url:    https://github.com/intel-lab-lkp/linux/commits/Javier-Martinez-Canillas/firmware-coreboot-Don-t-register-a-pdev-if-screen_info-data-is-present/20240914-053323
>> base:   https://git.kernel.org/pub/scm/linux/kernel/git/chrome-platform/linux.git for-next
>> patch link:    https://lore.kernel.org/r/20240913213246.1549213-1-javierm%40redhat.com
>> patch subject: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present
>> config: riscv-randconfig-001-20240915 (https://download.01.org/0day-ci/archive/20240915/202409151528.CIWZRPBq-lkp@intel.com/config)
>> compiler: clang version 15.0.7 (https://github.com/llvm/llvm-project 8dfdcc7b7bf66834a761bd8de445840ef68e4d1a)
>> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240915/202409151528.CIWZRPBq-lkp@intel.com/reproduce)
>>
>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>> the same patch/commit), kindly add following tags
>> | Reported-by: kernel test robot <lkp@intel.com>
>> | Closes: https://lore.kernel.org/oe-kbuild-all/202409151528.CIWZRPBq-lkp@intel.com/
>>
>> All errors (new ones prefixed by >>):
>>
>>>> ld.lld: error: undefined symbol: screen_info
>>     >>> referenced by framebuffer-coreboot.c:27 (drivers/firmware/google/framebuffer-coreboot.c:27)
>>     >>>               drivers/firmware/google/framebuffer-coreboot.o:(framebuffer_probe) in archive vmlinux.a
>>     >>> referenced by framebuffer-coreboot.c:27 (drivers/firmware/google/framebuffer-coreboot.c:27)
>>     >>>               drivers/firmware/google/framebuffer-coreboot.o:(framebuffer_probe) in archive vmlinux.a
>
> Not all platforms define screen_info. Maybe fix this by following

Yes, after reading the build errors reported by the robot I remembered
that we had similar issues with sysfb, for example commit 1260b9a7020
("drivers/firmware: fix SYSFB depends to prevent build failures") fixed
one of those.

> Tzung-Bi's advice of removing the local variables and then guard the
> test by CONFIG_SYSFB. If SYSFB has been defined, screen_info has to be 
> there. It's not a super pretty solution, though.
>

If possible I would prefer to avoid the ifdefery in the driver. I also
believe that the local variables makes the code easier to read. But if
you folks think that's better to drop them, I can do it in the next rev.

Another option is to restrict the architectures where this driver could
be build. As far as I understand it is mainly for x86 and ARM64 arches.

These two have a screen_info defined so the driver will build correctly.
I can include a preparatory patch that adds a "depends on x86 || ARM64".

> Best regards
> Thomas
>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat

Re: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present

[Thomas Zimmermann]

Hi Javier

Am 16.09.24 um 10:36 schrieb Javier Martinez Canillas:
> Thomas Zimmermann <tzimmermann@suse.de> writes:
>
> Hello Thomas and Tzung-Bi,
>
>> Hi
>>
>> Am 15.09.24 um 09:44 schrieb kernel test robot:
>>> Hi Javier,
>>>
>>> kernel test robot noticed the following build errors:
>>>
>>> [auto build test ERROR on chrome-platform/for-next]
>>> [also build test ERROR on chrome-platform/for-firmware-next linus/master v6.11-rc7 next-20240913]
>>> [If your patch is applied to the wrong git tree, kindly drop us a note.
>>> And when submitting patch, we suggest to use '--base' as documented in
>>> https://git-scm.com/docs/git-format-patch#_base_tree_information]
>>>
>>> url:    https://github.com/intel-lab-lkp/linux/commits/Javier-Martinez-Canillas/firmware-coreboot-Don-t-register-a-pdev-if-screen_info-data-is-present/20240914-053323
>>> base:   https://git.kernel.org/pub/scm/linux/kernel/git/chrome-platform/linux.git for-next
>>> patch link:    https://lore.kernel.org/r/20240913213246.1549213-1-javierm%40redhat.com
>>> patch subject: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present
>>> config: riscv-randconfig-001-20240915 (https://download.01.org/0day-ci/archive/20240915/202409151528.CIWZRPBq-lkp@intel.com/config)
>>> compiler: clang version 15.0.7 (https://github.com/llvm/llvm-project 8dfdcc7b7bf66834a761bd8de445840ef68e4d1a)
>>> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240915/202409151528.CIWZRPBq-lkp@intel.com/reproduce)
>>>
>>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>>> the same patch/commit), kindly add following tags
>>> | Reported-by: kernel test robot <lkp@intel.com>
>>> | Closes: https://lore.kernel.org/oe-kbuild-all/202409151528.CIWZRPBq-lkp@intel.com/
>>>
>>> All errors (new ones prefixed by >>):
>>>
>>>>> ld.lld: error: undefined symbol: screen_info
>>>      >>> referenced by framebuffer-coreboot.c:27 (drivers/firmware/google/framebuffer-coreboot.c:27)
>>>      >>>               drivers/firmware/google/framebuffer-coreboot.o:(framebuffer_probe) in archive vmlinux.a
>>>      >>> referenced by framebuffer-coreboot.c:27 (drivers/firmware/google/framebuffer-coreboot.c:27)
>>>      >>>               drivers/firmware/google/framebuffer-coreboot.o:(framebuffer_probe) in archive vmlinux.a
>> Not all platforms define screen_info. Maybe fix this by following
> Yes, after reading the build errors reported by the robot I remembered
> that we had similar issues with sysfb, for example commit 1260b9a7020
> ("drivers/firmware: fix SYSFB depends to prevent build failures") fixed
> one of those.
>
>> Tzung-Bi's advice of removing the local variables and then guard the
>> test by CONFIG_SYSFB. If SYSFB has been defined, screen_info has to be
>> there. It's not a super pretty solution, though.
>>
> If possible I would prefer to avoid the ifdefery in the driver. I also
> believe that the local variables makes the code easier to read. But if
> you folks think that's better to drop them, I can do it in the next rev.
>
> Another option is to restrict the architectures where this driver could
> be build. As far as I understand it is mainly for x86 and ARM64 arches.
>
> These two have a screen_info defined so the driver will build correctly.
> I can include a preparatory patch that adds a "depends on x86 || ARM64".

That feels arbitrary, as the dependency is not really in coreboot, but 
in sysbf. What you'd want is a HAVE_SCREEN_INFO define on the 
architectures that provide it. IIRC earlier attempts to add this have 
failed. :/

If you don't want the ifdef-ery in coreboot.c, you could add a helper to 
sysfb. Let's say

   bool sysfb_handles_screen_info(void)

returns the result of the test. If you put it next to sysfb_disable(), 
you could add an empty wrapper into the sysfb.h header as well. [1]

(There's still the possibility that screen_info is available, but sysfb 
has been disabled. But that's not different from how it currently works.)

[1] 
https://elixir.bootlin.com/linux/v6.10.10/source/include/linux/sysfb.h#L65

Best regards
Thomas

>
>> Best regards
>> Thomas
>>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

Re: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present

[Javier Martinez Canillas]

Thomas Zimmermann <tzimmermann@suse.de> writes:

Hello Thomas,

> Hi Javier
>
> Am 16.09.24 um 10:36 schrieb Javier Martinez Canillas:
>> Thomas Zimmermann <tzimmermann@suse.de> writes:
>>
>> Hello Thomas and Tzung-Bi,
>>
>>> Hi
>>>
>>> Am 15.09.24 um 09:44 schrieb kernel test robot:
>>>> Hi Javier,
>>>>
>>>> kernel test robot noticed the following build errors:
>>>>
>>>> [auto build test ERROR on chrome-platform/for-next]
>>>> [also build test ERROR on chrome-platform/for-firmware-next linus/master v6.11-rc7 next-20240913]
>>>> [If your patch is applied to the wrong git tree, kindly drop us a note.
>>>> And when submitting patch, we suggest to use '--base' as documented in
>>>> https://git-scm.com/docs/git-format-patch#_base_tree_information]
>>>>
>>>> url:    https://github.com/intel-lab-lkp/linux/commits/Javier-Martinez-Canillas/firmware-coreboot-Don-t-register-a-pdev-if-screen_info-data-is-present/20240914-053323
>>>> base:   https://git.kernel.org/pub/scm/linux/kernel/git/chrome-platform/linux.git for-next
>>>> patch link:    https://lore.kernel.org/r/20240913213246.1549213-1-javierm%40redhat.com
>>>> patch subject: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present
>>>> config: riscv-randconfig-001-20240915 (https://download.01.org/0day-ci/archive/20240915/202409151528.CIWZRPBq-lkp@intel.com/config)
>>>> compiler: clang version 15.0.7 (https://github.com/llvm/llvm-project 8dfdcc7b7bf66834a761bd8de445840ef68e4d1a)
>>>> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240915/202409151528.CIWZRPBq-lkp@intel.com/reproduce)
>>>>
>>>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>>>> the same patch/commit), kindly add following tags
>>>> | Reported-by: kernel test robot <lkp@intel.com>
>>>> | Closes: https://lore.kernel.org/oe-kbuild-all/202409151528.CIWZRPBq-lkp@intel.com/
>>>>
>>>> All errors (new ones prefixed by >>):
>>>>
>>>>>> ld.lld: error: undefined symbol: screen_info
>>>>      >>> referenced by framebuffer-coreboot.c:27 (drivers/firmware/google/framebuffer-coreboot.c:27)
>>>>      >>>               drivers/firmware/google/framebuffer-coreboot.o:(framebuffer_probe) in archive vmlinux.a
>>>>      >>> referenced by framebuffer-coreboot.c:27 (drivers/firmware/google/framebuffer-coreboot.c:27)
>>>>      >>>               drivers/firmware/google/framebuffer-coreboot.o:(framebuffer_probe) in archive vmlinux.a
>>> Not all platforms define screen_info. Maybe fix this by following
>> Yes, after reading the build errors reported by the robot I remembered
>> that we had similar issues with sysfb, for example commit 1260b9a7020
>> ("drivers/firmware: fix SYSFB depends to prevent build failures") fixed
>> one of those.
>>
>>> Tzung-Bi's advice of removing the local variables and then guard the
>>> test by CONFIG_SYSFB. If SYSFB has been defined, screen_info has to be
>>> there. It's not a super pretty solution, though.
>>>
>> If possible I would prefer to avoid the ifdefery in the driver. I also
>> believe that the local variables makes the code easier to read. But if
>> you folks think that's better to drop them, I can do it in the next rev.
>>
>> Another option is to restrict the architectures where this driver could
>> be build. As far as I understand it is mainly for x86 and ARM64 arches.
>>
>> These two have a screen_info defined so the driver will build correctly.
>> I can include a preparatory patch that adds a "depends on x86 || ARM64".
>
> That feels arbitrary, as the dependency is not really in coreboot, but 
> in sysbf. What you'd want is a HAVE_SCREEN_INFO define on the 
> architectures that provide it. IIRC earlier attempts to add this have 
> failed. :/
>
> If you don't want the ifdef-ery in coreboot.c, you could add a helper to 
> sysfb. Let's say
>
>    bool sysfb_handles_screen_info(void)
>
> returns the result of the test. If you put it next to sysfb_disable(), 
> you could add an empty wrapper into the sysfb.h header as well. [1]
>
> (There's still the possibility that screen_info is available, but sysfb 
> has been disabled. But that's not different from how it currently works.)
>

I like that. And when SYSFB is not enabled, sysfb_handles_screen_info()
could just be defined as "return false;" which will indicate to drivers
that would have to handle the system frambuffer themselves.

I'll try to type the patches later today.

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat