linux-kernel - Re: [PATCH v2 1/2] drm: Add a drm_drv_enabled() to check if drivers should be enabled

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Message-ID: <0c07f121-42d3-9f37-1e14-842fb685b501@redhat.com>
Date:   Thu, 4 Nov 2021 21:09:14 +0100
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Cc:     Michel Dänzer <michel@...nzer.net>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Peter Robinson <pbrobinson@...il.com>,
        Pekka Paalanen <pekka.paalanen@...labora.com>,
        Alex Deucher <alexander.deucher@....com>,
        Ben Skeggs <bskeggs@...hat.com>, Chia-I Wu <olvaffe@...il.com>,
        Christian König <christian.koenig@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Airlie <airlied@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        VMware Graphics <linux-graphics-maintainer@...are.com>,
        Zack Rusin <zackr@...are.com>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        nouveau@...ts.freedesktop.org, spice-devel@...ts.freedesktop.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 1/2] drm: Add a drm_drv_enabled() to check if drivers
 should be enabled

Hello Jani,

On 11/4/21 20:57, Jani Nikula wrote:
> On Thu, 04 Nov 2021, Javier Martinez Canillas <javierm@...hat.com> wrote:
>> +/**
>> + * 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.
>> + *
>> + * Return: 0 on success or a negative error code on failure.
>> + */
>> +int drm_drv_enabled(const struct drm_driver *driver)
>> +{
>> +	if (vgacon_text_force()) {
>> +		DRM_INFO("%s driver is disabled\n", driver->name);
>> +		return -ENODEV;
>> +	}
>> +
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL(drm_drv_enabled);
> 
> The name implies a bool return, but it's not.
> 
> 	if (drm_drv_enabled(...)) {
> 		/* surprise, it's disabled! */
> 	}
> 

It used to return a bool in v2 but Thomas suggested an int instead to
have consistency on the errno code that was returned by the callers.

I should probably name that function differently to avoid confusion.

But I think you are correct and this change is caused too much churn
for not that much benefit, specially since is unclear that there might
be another condition to prevent a DRM driver to load besides nomodeset.

I'll just drop this patch and post only #2 but making drivers to test
using the drm_check_modeset() function (which doesn't have a name that
implies a bool return).

> 
> BR,
> Jani.
> 
> 
> 

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat