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Date: Sat, 10 Feb 2024 23:19:23 -0600
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Subject: Re: [PATCH v4 1/3] drm: Add drm_get_acpi_edid() helper
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To: Jani Nikula <jani.nikula@linux.intel.com>, amd-gfx@lists.freedesktop.org,
 "open list:DRM DRIVERS" <dri-devel@lists.freedesktop.org>,
 "open list:ACPI" <linux-acpi@vger.kernel.org>,
 open list <linux-kernel@vger.kernel.org>, Melissa Wen <mwen@igalia.com>,
 Dave Airlie <airlied@redhat.com>, Maxime Ripard <mripard@kernel.org>,
 Thomas Zimmermann <tzimmermann@suse.de>,
 Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
References: <20240207224429.104625-1-mario.limonciello@amd.com>
 <20240207224429.104625-2-mario.limonciello@amd.com>
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 <9fa0c1ad-dd7d-4350-aad1-4723450850bd@amd.com>
 <ZcZ1tdXqH90RabvV@phenom.ffwll.local>
From: Mario Limonciello <mario.limonciello@amd.com>
In-Reply-To: <ZcZ1tdXqH90RabvV@phenom.ffwll.local>
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On 2/9/2024 12:57, Daniel Vetter wrote:
> On Fri, Feb 09, 2024 at 09:34:13AM -0600, Mario Limonciello wrote:
>> On 2/9/2024 05:07, Daniel Vetter wrote:
>>> On Thu, Feb 08, 2024 at 11:57:11AM +0200, Jani Nikula wrote:
>>>> On Wed, 07 Feb 2024, Mario Limonciello <mario.limonciello@amd.com> wrote:
>>>>> Some manufacturers have intentionally put an EDID that differs from
>>>>> the EDID on the internal panel on laptops.  Drivers can call this
>>>>> helper to attempt to fetch the EDID from the BIOS's ACPI _DDC method.
>>>>>
>>>>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
>>>>> ---
>>>>>    drivers/gpu/drm/Kconfig    |  5 +++
>>>>>    drivers/gpu/drm/drm_edid.c | 77 ++++++++++++++++++++++++++++++++++++++
>>>>>    include/drm/drm_edid.h     |  1 +
>>>>>    3 files changed, 83 insertions(+)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
>>>>> index 6ec33d36f3a4..ec2bb71e8b36 100644
>>>>> --- a/drivers/gpu/drm/Kconfig
>>>>> +++ b/drivers/gpu/drm/Kconfig
>>>>> @@ -21,6 +21,11 @@ menuconfig DRM
>>>>>    	select KCMP
>>>>>    	select VIDEO_CMDLINE
>>>>>    	select VIDEO_NOMODESET
>>>>> +	select ACPI_VIDEO if ACPI
>>>>> +	select BACKLIGHT_CLASS_DEVICE if ACPI
>>>>> +	select INPUT if ACPI
>>>>> +	select X86_PLATFORM_DEVICES if ACPI && X86
>>>>> +	select ACPI_WMI if ACPI && X86
>>>>
>>>> I think I'll defer to drm maintainers on whether this is okay or
>>>> something to be avoided.
>>>
>>> Uh yeah this is a bit much, and select just messes with everything. Just
>>> #ifdef this in the code with a dummy alternative, if users configure their
>>> kernel without acpi but need it, they get to keep all the pieces.
>>>
>>> Alternatively make a DRM_ACPI_HELPERS symbol, but imo a Kconfig for every
>>> function is also not great. And just using #ifdef in the code also works
>>> for CONFIG_OF, which is exactly the same thing for platforms using dt to
>>> describe hw.
>>>
>>> Also I'd expect ACPI code to already provide dummy functions if ACPI is
>>> provided, so you probably dont even need all that much #ifdef in the code.
>>>
>>> What we defo cant do is select platform/hw stuff just because you enable
>>> CONFIG_DRM.
>>> -Sima
>>
>> The problem was with linking.  I'll experiment with #ifdef for the next
>> version.
> 
> Ah yes, if e.g. acpi is a module but drm is built-in then it will compile,
> but not link.
> 
> You need
> 
> 	depends on (ACPI || ACPI=n)
> 
> for this. Looks a bit funny but works for all combinations.

Nope; this fails at link time with this combination:

CONFIG_ACPI=y
CONFIG_ACPI_VIDEO=m
CONFIG_DRM=y

ld: drivers/gpu/drm/drm_edid.o: in function `drm_do_probe_acpi_edid':
drm_edid.c:(.text+0xd34): undefined reference to `acpi_video_get_edid'
make[5]: *** [scripts/Makefile.vmlinux:37: vmlinux] Error 1

So the logical solution is to try
	depends on (ACPI_VIDEO || ACPI_VIDEO=n)

But that leads me back to the rabbit hole of why I had the selects moved 
to drm instead of drivers in the first place:

drivers/gpu/drm/Kconfig:8:error: recursive dependency detected!
drivers/gpu/drm/Kconfig:8:      symbol DRM depends on ACPI_VIDEO
drivers/acpi/Kconfig:213:       symbol ACPI_VIDEO depends on 
BACKLIGHT_CLASS_DEVICE
drivers/video/backlight/Kconfig:136:    symbol BACKLIGHT_CLASS_DEVICE is 
selected by DRM_RADEON
drivers/gpu/drm/radeon/Kconfig:3:       symbol DRM_RADEON depends on DRM


> 
> Since this gets mess it might be useful to have a DRM_ACPI_HELPERS Kconfig
> that controls all this.

How about all those selects that I had in this patch moved to 
DRM_ACPI_HELPERS and keep the patch that drops from all the drivers then?

> -Sima
> 
>>
>>>
>>>>
>>>>
>>>>>    	help
>>>>>    	  Kernel-level support for the Direct Rendering Infrastructure (DRI)
>>>>>    	  introduced in XFree86 4.0. If you say Y here, you need to select
>>>>> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
>>>>> index 923c4423151c..c649b4f9fd8e 100644
>>>>> --- a/drivers/gpu/drm/drm_edid.c
>>>>> +++ b/drivers/gpu/drm/drm_edid.c
>>>>> @@ -28,6 +28,7 @@
>>>>>     * DEALINGS IN THE SOFTWARE.
>>>>>     */
>>>>> +#include <acpi/video.h>
>>>>>    #include <linux/bitfield.h>
>>>>>    #include <linux/cec.h>
>>>>>    #include <linux/hdmi.h>
>>>>> @@ -2188,6 +2189,49 @@ drm_do_probe_ddc_edid(void *data, u8 *buf, unsigned int block, size_t len)
>>>>>    	return ret == xfers ? 0 : -1;
>>>>>    }
>>>>> +/**
>>>>> + * drm_do_probe_acpi_edid() - get EDID information via ACPI _DDC
>>>>> + * @data: struct drm_device
>>>>> + * @buf: EDID data buffer to be filled
>>>>> + * @block: 128 byte EDID block to start fetching from
>>>>> + * @len: EDID data buffer length to fetch
>>>>> + *
>>>>> + * Try to fetch EDID information by calling acpi_video_get_edid() function.
>>>>> + *
>>>>> + * Return: 0 on success or error code on failure.
>>>>> + */
>>>>> +static int
>>>>> +drm_do_probe_acpi_edid(void *data, u8 *buf, unsigned int block, size_t len)
>>>>> +{
>>>>> +	struct drm_device *ddev = data;
>>>>> +	struct acpi_device *acpidev = ACPI_COMPANION(ddev->dev);
>>>>> +	unsigned char start = block * EDID_LENGTH;
>>>>> +	void *edid;
>>>>> +	int r;
>>>>> +
>>>>> +	if (!acpidev)
>>>>> +		return -ENODEV;
>>>>> +
>>>>> +	/* fetch the entire edid from BIOS */
>>>>> +	r = acpi_video_get_edid(acpidev, ACPI_VIDEO_DISPLAY_LCD, -1, &edid);
>>>>> +	if (r < 0) {
>>>>> +		DRM_DEBUG_KMS("Failed to get EDID from ACPI: %d\n", r);
>>>>> +		return -EINVAL;
>>>>> +	}
>>>>> +	if (len > r || start > r || start + len > r) {
>>>>> +		r = -EINVAL;
>>>>> +		goto cleanup;
>>>>> +	}
>>>>> +
>>>>> +	memcpy(buf, edid + start, len);
>>>>> +	r = 0;
>>>>> +
>>>>> +cleanup:
>>>>> +	kfree(edid);
>>>>> +
>>>>> +	return r;
>>>>> +}
>>>>> +
>>>>>    static void connector_bad_edid(struct drm_connector *connector,
>>>>>    			       const struct edid *edid, int num_blocks)
>>>>>    {
>>>>> @@ -2643,6 +2687,39 @@ struct edid *drm_get_edid(struct drm_connector *connector,
>>>>>    }
>>>>>    EXPORT_SYMBOL(drm_get_edid);
>>>>> +/**
>>>>> + * drm_get_acpi_edid - get EDID data, if available
>>>>
>>>> I'd prefer all the new EDID API to be named drm_edid_*. Makes a clean
>>>> break from the old API, and is more consistent.
>>>>
>>>> So perhaps drm_edid_read_acpi() to be in line with all the other struct
>>>> drm_edid based EDID reading functions.
>>>>
>>>>> + * @connector: connector we're probing
>>>>> + *
>>>>> + * Use the BIOS to attempt to grab EDID data if possible.
>>>>> + *
>>>>> + * The returned pointer must be freed using drm_edid_free().
>>>>> + *
>>>>> + * Return: Pointer to valid EDID or NULL if we couldn't find any.
>>>>> + */
>>>>> +const struct drm_edid *drm_get_acpi_edid(struct drm_connector *connector)
>>>>> +{
>>>>> +	const struct drm_edid *drm_edid;
>>>>> +
>>>>> +	switch (connector->connector_type) {
>>>>> +	case DRM_MODE_CONNECTOR_LVDS:
>>>>> +	case DRM_MODE_CONNECTOR_eDP:
>>>>> +		break;
>>>>> +	default:
>>>>> +		return NULL;
>>>>> +	}
>>>>> +
>>>>> +	if (connector->force == DRM_FORCE_OFF)
>>>>> +		return NULL;
>>>>> +
>>>>> +	drm_edid = drm_edid_read_custom(connector, drm_do_probe_acpi_edid, connector->dev);
>>>>> +
>>>>> +	/* Note: Do *not* call connector updates here. */
>>>>> +
>>>>> +	return drm_edid;
>>>>> +}
>>>>> +EXPORT_SYMBOL(drm_get_acpi_edid);
>>>>> +
>>>>>    /**
>>>>>     * drm_edid_read_custom - Read EDID data using given EDID block read function
>>>>>     * @connector: Connector to use
>>>>> diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
>>>>> index 7923bc00dc7a..ca41be289fc6 100644
>>>>> --- a/include/drm/drm_edid.h
>>>>> +++ b/include/drm/drm_edid.h
>>>>> @@ -410,6 +410,7 @@ struct edid *drm_do_get_edid(struct drm_connector *connector,
>>>>>    	void *data);
>>>>>    struct edid *drm_get_edid(struct drm_connector *connector,
>>>>>    			  struct i2c_adapter *adapter);
>>>>> +const struct drm_edid *drm_get_acpi_edid(struct drm_connector *connector);
>>>>
>>>> There's a comment
>>>>
>>>> /* Interface based on struct drm_edid */
>>>>
>>>> towards the end of the file, gathering all the new API under it.
>>>>
>>>> Other than that, LGTM,
>>>>
>>>> BR,
>>>> Jani.
>>>>
>>>>>    u32 drm_edid_get_panel_id(struct i2c_adapter *adapter);
>>>>>    struct edid *drm_get_edid_switcheroo(struct drm_connector *connector,
>>>>>    				     struct i2c_adapter *adapter);
>>>>
>>>> -- 
>>>> Jani Nikula, Intel
>>>
>>
>