Re: [PATCH] drm/vmwgfx: respect 'nomodeset'

[Thomas Hellstrom <thellstrom@vmware.com>]

On 10/15/2014 10:51 PM, Rob Clark wrote:
> On Wed, Oct 15, 2014 at 4:44 PM, Thomas Hellstrom <thellstrom@vmware.com> wrote:
>> On 10/15/2014 10:38 PM, Rob Clark wrote:
>>> On Wed, Oct 15, 2014 at 4:35 PM, Rob Clark <robdclark@gmail.com> wrote:
>>>> On Wed, Oct 15, 2014 at 4:17 PM, Thomas Hellstrom <thellstrom@vmware.com> wrote:
>>>>> On 10/15/2014 09:46 PM, Rob Clark wrote:
>>>>>> On Wed, Oct 15, 2014 at 3:24 PM, Thomas Hellstrom <thellstrom@vmware.com> wrote:
>>>>>>> On 10/15/2014 09:00 PM, Rob Clark wrote:
>>>>>>>> Signed-off-by: Rob Clark <robdclark@gmail.com>
>>>>>>>> ---
>>>>>>>>  drivers/gpu/drm/vmwgfx/vmwgfx_drv.c | 7 +++++++
>>>>>>>>  1 file changed, 7 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
>>>>>>>> index 18b54ac..f0267b8 100644
>>>>>>>> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
>>>>>>>> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
>>>>>>>> @@ -25,6 +25,7 @@
>>>>>>>>   *
>>>>>>>>   **************************************************************************/
>>>>>>>>  #include <linux/module.h>
>>>>>>>> +#include <linux/console.h>
>>>>>>>>
>>>>>>>>  #include <drm/drmP.h>
>>>>>>>>  #include "vmwgfx_drv.h"
>>>>>>>> @@ -1453,6 +1454,12 @@ static int vmw_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>>>>>>>>  static int __init vmwgfx_init(void)
>>>>>>>>  {
>>>>>>>>       int ret;
>>>>>>>> +
>>>>>>>> +#ifdef CONFIG_VGA_CONSOLE
>>>>>>>> +     if (vgacon_text_force())
>>>>>>>> +             return -EINVAL;
>>>>>>>> +#endif
>>>>>>>> +
>>>>>>> Hmm,
>>>>>>>
>>>>>>> From the function name vgacon_text_force() it sounds like this should
>>>>>>> just stop the driver from initializing fbcon? Not refuse to load?
>>>>>> yeah, the function is badly named.. it perhaps should be
>>>>>> vgacon_is_text_forced() or something like that.  But basically it
>>>>>> returns whether we are forced to text mode.
>>>>>>
>>>>>> BR,
>>>>>> -R
>>>>> So then I guess it would be more correct to use the output of that
>>>>> function when determining the value of dev_priv->enable_fb (vmwgfx can
>>>>> enable the user-space modesetting API without turning on vmwgfx fbcon).
>>>> well, other drivers, 'nomodeset' forces the driver not to load (to
>>>> work around buggyness, etc)..  I suppose for vmwgfx perhaps oddball
>>>> "hardware" is less of a concern.  Although it seems like it would be
>>>> nice if vmwgfx behaved consistently with the other drivers.
>>>>
>>>> Most/all for the drivers have an additional module param that lets you
>>>> override this and load the driver for UMS in case of 'nomodeset'..
>>>> which would give you the behaviour you describe.  But I think in the
>>>> absence of an additional module param specified, the default
>>>> 'nomodeset' behaviour should be that the driver does not load.
>>>>
>>>> But I can add such a module param if you think it is useful..
>>> oh, wait.. you already have an 'enable_fbdev'..  although I guess that
>>> is actually meaning "enable_kms"?
>> It should actually have been "enable_fbcon_and_fbdev" instead of
>> "enable_fbdev". KMS is always enabled with the vmwgfx driver, we have no
>> UMS driver using DRM functionality.
>>
>> I think what confuses me is how "nomodeset" translates to
>> "use_text_console", (sounds orthogonal to me) but if that's the way that
>> parameter is presented to the drivers, I guess the correct way after all
>> is to stop the driver from loading....
> the:
>
>   __setup("nomodeset", text_mode);
>
> bit causes text_mode() to be called which sets vgacon_text_mode_force
>
> (assuming that was the question)
Yes. Then IMHO whoever wrote that didn't do his homework since you can
have user-space modesetting API and a text mode console working
perfectly well together, but never mind.

>At least users seem to expect that 'nomodeset' means don't load the
modesetting driver, since I got a bug about it ;-) BR, -R

I agree.
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>.

I'll include the patch in the next pull request.

Thanks,
Thomas



>> /Thomas
>>