linux-kernel - Re: [RESEND PATCH 4/5] drm: Add a drm_drv

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Date:   Thu, 04 Nov 2021 13:10:48 +0200
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     Pekka Paalanen <pekka.paalanen@...labora.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Michel Dänzer <michel@...nzer.net>,
        dri-devel@...ts.freedesktop.org,
        Peter Robinson <pbrobinson@...il.com>,
        Neal Gompa <ngompa13@...il.com>
Subject: Re: [RESEND PATCH 4/5] drm: Add a drm_drv_enabled() helper function

On Wed, 03 Nov 2021, Thomas Zimmermann <tzimmermann@...e.de> wrote:
> Hi
>
> Am 03.11.21 um 14:41 schrieb Jani Nikula:
>> On Wed, 03 Nov 2021, Javier Martinez Canillas <javierm@...hat.com> wrote:
>>> DRM drivers can use this to determine whether they can be enabled or not.
>>>
>>> For now it's just a wrapper around drm_modeset_disabled() but having the
>>> indirection level will allow to add other conditions besides "nomodeset".
>>>
>>> Suggested-by: Thomas Zimmermann <tzimmermann@...e.de>
>>> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
>> 
>> Can't see i915 trivially using this due to the drm_driver
>> parameter. Please let's not merge helpers like this without actual
>> users.
>
> Can you explain?
>
> This would be called on the top of the PCI probe function. The parameter 
> would allow to decide on a per-driver base (e.g., to ignore generic 
> drivers).

Where and how exactly? This is why we need to see the patch using the
function. A patch is worth a thousand words. ;)

See current vgacon_text_force() usage in i915/i915_module.c. It happens
way before anything related to pci or drm driver. Why bother with the
complicated setup and teardown of stuff if you can bail out earlier?


BR,
Jani.

>
> Best regards
> Thomas
>
>> 
>> BR,
>> Jani.
>> 
>> 
>>> ---
>>>
>>>   drivers/gpu/drm/drm_drv.c | 21 +++++++++++++++++++++
>>>   include/drm/drm_drv.h     |  1 +
>>>   2 files changed, 22 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
>>> index 8214a0b1ab7f..70ef08941e06 100644
>>> --- a/drivers/gpu/drm/drm_drv.c
>>> +++ b/drivers/gpu/drm/drm_drv.c
>>> @@ -975,6 +975,27 @@ int drm_dev_set_unique(struct drm_device *dev, const char *name)
>>>   }
>>>   EXPORT_SYMBOL(drm_dev_set_unique);
>>>   
>>> +/**
>>> + * drm_drv_enabled - Checks if a DRM driver can be enabled
>>> + * @driver: DRM driver to check
>>> + *
>>> + * Checks whether a DRM driver can be enabled or not. This may be the case
>>> + * if the "nomodeset" kernel command line parameter is used.
>>> + *
>>> + * Returns:
>>> + * True if the DRM driver is enabled and false otherwise.
>>> + */
>>> +bool drm_drv_enabled(const struct drm_driver *driver)
>>> +{
>>> +	if (drm_modeset_disabled()) {
>>> +		DRM_INFO("%s driver is disabled\n", driver->name);
>>> +		return false;
>>> +	}
>>> +
>>> +	return true;
>>> +}
>>> +EXPORT_SYMBOL(drm_drv_enabled);
>>> +
>>>   /*
>>>    * DRM Core
>>>    * The DRM core module initializes all global DRM objects and makes them
>>> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
>>> index 0cd95953cdf5..48f2b6eec012 100644
>>> --- a/include/drm/drm_drv.h
>>> +++ b/include/drm/drm_drv.h
>>> @@ -598,5 +598,6 @@ static inline bool drm_drv_uses_atomic_modeset(struct drm_device *dev)
>>>   
>>>   int drm_dev_set_unique(struct drm_device *dev, const char *name);
>>>   
>>> +bool drm_drv_enabled(const struct drm_driver *driver);
>>>   
>>>   #endif
>> 

-- 
Jani Nikula, Intel Open Source Graphics Center