by Jyri Sarha

[permalink] [raw]

Subject: Re: [PATCH v2 36/37] drm/tilcdc: Add support for the nomodeset kernel parameter

On 2021-12-17 2:37, Javier Martinez Canillas wrote:
> According to disable Documentation/admin-guide/kernel-parameters.txt,
> this
> parameter can be used to disable kernel modesetting.
>
> DRM drivers will not perform display-mode changes or accelerated
> rendering
> and only the system framebuffer will be available if it was set-up.
>
> But only a few DRM drivers currently check for nomodeset, make this
> driver
> to also support the command line parameter.
>
> Signed-off-by: Javier Martinez Canillas <[email protected]>

Acked-by: Jyri Sarha <[email protected]>

> ---
>
> (no changes since v1)
>
> drivers/gpu/drm/tilcdc/tilcdc_drv.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/tilcdc/tilcdc_drv.c
> b/drivers/gpu/drm/tilcdc/tilcdc_drv.c
> index cc567c87057d..eee3c447fbac 100644
> --- a/drivers/gpu/drm/tilcdc/tilcdc_drv.c
> +++ b/drivers/gpu/drm/tilcdc/tilcdc_drv.c
> @@ -604,6 +604,9 @@ static struct platform_driver
> tilcdc_platform_driver = {
>
> static int __init tilcdc_drm_init(void)
> {
> + if (drm_firmware_drivers_only())
> + return -ENODEV;
> +
> DBG("init");
> tilcdc_panel_init();
> return platform_driver_register(&tilcdc_platform_driver);

2021-12-17 14:32:07

Hi

Am 28.01.22 um 10:13 schrieb Kieran Bingham:
> Hi Javier,
>
> Quoting Javier Martinez Canillas (2021-12-17 00:37:46)
>> According to disable Documentation/admin-guide/kernel-parameters.txt, this
>> parameter can be used to disable kernel modesetting.
>>
>> DRM drivers will not perform display-mode changes or accelerated rendering
>> and only the system framebuffer will be available if it was set-up.
>
> What is the 'system framebuffer' in this instance? Reading
> https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.txt
> it sounds like that means anything already set up by the bootloader.

Exactly this.

>
>> But only a few DRM drivers currently check for nomodeset, make this driver
>> to also support the command line parameter.
>>
>> Signed-off-by: Javier Martinez Canillas <[email protected]>
>> ---
>>
>> (no changes since v1)
>>
>> drivers/gpu/drm/rcar-du/rcar_du_drv.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_drv.c b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
>> index 5a8131ef81d5..982e450233ed 100644
>> --- a/drivers/gpu/drm/rcar-du/rcar_du_drv.c
>> +++ b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
>> @@ -701,6 +701,9 @@ static struct platform_driver rcar_du_platform_driver = {
>>
>> static int __init rcar_du_init(void)
>> {
>> + if (drm_firmware_drivers_only())
>> + return -ENODEV;
>> +
>
> This will completely disable all control of the display device when
> nomodeset is enabled.
>
> Is there any requirement for us to support outputting to the display if
> it was previously set up? presumably without setting or changing any
> modes, but simply allowing the existing frame to be updated?

There's no requirement for your driver. We just want a parameter where
we can conveniently disable most of DRM's drivers and reduce it to a
minimum. Helps distributions to provide a simple fallback mode. Most
PCI-based drivers already support that. Now we're added it to the other
drivers as well.

>
> I think the implication is that 'firmware drivers' would mean a display
> could be updated through some firmware interface, which we won't have
> ... so it seems reasonable to accept that this whole driver can be
> disabled in that instance.

It cannot be 'mode-setted'. We get a pre-configured framebuffer from the
firmware or bootloader. Whatever we draw there shows up on the screen.

Best regards
Thomas

>
> Reading your mail that brought this thread up in my inbox, I think
> you've already hit merge on this, so don't worry about adding a tag in
> that instance, but I think this is ok.
>
> Reviewed-by: Kieran Bingham <[email protected]>
>
>> rcar_du_of_init(rcar_du_of_table);
>>
>> return platform_driver_register(&rcar_du_platform_driver);
>> --
>> 2.33.1
>>

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

Attachments:

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2022-01-30 23:39:57

by Laurent Pinchart

[permalink] [raw]

Subject: Re: [PATCH v2 31/37] drm: rcar-du: Add support for the nomodeset kernel parameter

Hi Thomas,

On Fri, Jan 28, 2022 at 10:33:21AM +0100, Thomas Zimmermann wrote:
> Am 28.01.22 um 10:13 schrieb Kieran Bingham:
> > Quoting Javier Martinez Canillas (2021-12-17 00:37:46)
> >> According to disable Documentation/admin-guide/kernel-parameters.txt, this
> >> parameter can be used to disable kernel modesetting.
> >>
> >> DRM drivers will not perform display-mode changes or accelerated rendering
> >> and only the system framebuffer will be available if it was set-up.
> >
> > What is the 'system framebuffer' in this instance? Reading
> > https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.txt
> > it sounds like that means anything already set up by the bootloader.
>
> Exactly this.
>
> >> But only a few DRM drivers currently check for nomodeset, make this driver
> >> to also support the command line parameter.
> >>
> >> Signed-off-by: Javier Martinez Canillas <[email protected]>
> >> ---
> >>
> >> (no changes since v1)
> >>
> >> drivers/gpu/drm/rcar-du/rcar_du_drv.c | 3 +++
> >> 1 file changed, 3 insertions(+)
> >>
> >> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_drv.c b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
> >> index 5a8131ef81d5..982e450233ed 100644
> >> --- a/drivers/gpu/drm/rcar-du/rcar_du_drv.c
> >> +++ b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
> >> @@ -701,6 +701,9 @@ static struct platform_driver rcar_du_platform_driver = {
> >>
> >> static int __init rcar_du_init(void)
> >> {
> >> + if (drm_firmware_drivers_only())
> >> + return -ENODEV;
> >> +
> >
> > This will completely disable all control of the display device when
> > nomodeset is enabled.
> >
> > Is there any requirement for us to support outputting to the display if
> > it was previously set up? presumably without setting or changing any
> > modes, but simply allowing the existing frame to be updated?
>
> There's no requirement for your driver. We just want a parameter where
> we can conveniently disable most of DRM's drivers and reduce it to a
> minimum. Helps distributions to provide a simple fallback mode. Most
> PCI-based drivers already support that. Now we're added it to the other
> drivers as well.
>
> >
> > I think the implication is that 'firmware drivers' would mean a display
> > could be updated through some firmware interface, which we won't have
> > ... so it seems reasonable to accept that this whole driver can be
> > disabled in that instance.
>
> It cannot be 'mode-setted'. We get a pre-configured framebuffer from the
> firmware or bootloader. Whatever we draw there shows up on the screen.

I doubt that's going to work as you expect, clocks and regulators will
get disabled at boot if not used by any driver.

> > Reading your mail that brought this thread up in my inbox, I think
> > you've already hit merge on this, so don't worry about adding a tag in
> > that instance, but I think this is ok.
> >
> > Reviewed-by: Kieran Bingham <[email protected]>
> >
> >> rcar_du_of_init(rcar_du_of_table);
> >>
> >> return platform_driver_register(&rcar_du_platform_driver);

--
Regards,

Laurent Pinchart

2022-01-30 23:41:19

by Laurent Pinchart

[permalink] [raw]

Subject: Re: [PATCH v2 31/37] drm: rcar-du: Add support for the nomodeset kernel parameter

Hi Thomas,

On Fri, Jan 28, 2022 at 11:46:49AM +0100, Thomas Zimmermann wrote:
> Am 28.01.22 um 11:34 schrieb Laurent Pinchart:
> > On Fri, Jan 28, 2022 at 10:33:21AM +0100, Thomas Zimmermann wrote:
> >> Am 28.01.22 um 10:13 schrieb Kieran Bingham:
> >>> Quoting Javier Martinez Canillas (2021-12-17 00:37:46)
> >>>> According to disable Documentation/admin-guide/kernel-parameters.txt, this
> >>>> parameter can be used to disable kernel modesetting.
> >>>>
> >>>> DRM drivers will not perform display-mode changes or accelerated rendering
> >>>> and only the system framebuffer will be available if it was set-up.
> >>>
> >>> What is the 'system framebuffer' in this instance? Reading
> >>> https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.txt
> >>> it sounds like that means anything already set up by the bootloader.
> >>
> >> Exactly this.
> >>
> >>>> But only a few DRM drivers currently check for nomodeset, make this driver
> >>>> to also support the command line parameter.
> >>>>
> >>>> Signed-off-by: Javier Martinez Canillas <[email protected]>
> >>>> ---
> >>>>
> >>>> (no changes since v1)
> >>>>
> >>>> drivers/gpu/drm/rcar-du/rcar_du_drv.c | 3 +++
> >>>> 1 file changed, 3 insertions(+)
> >>>>
> >>>> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_drv.c b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
> >>>> index 5a8131ef81d5..982e450233ed 100644
> >>>> --- a/drivers/gpu/drm/rcar-du/rcar_du_drv.c
> >>>> +++ b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
> >>>> @@ -701,6 +701,9 @@ static struct platform_driver rcar_du_platform_driver = {
> >>>>
> >>>> static int __init rcar_du_init(void)
> >>>> {
> >>>> + if (drm_firmware_drivers_only())
> >>>> + return -ENODEV;
> >>>> +
> >>>
> >>> This will completely disable all control of the display device when
> >>> nomodeset is enabled.
> >>>
> >>> Is there any requirement for us to support outputting to the display if
> >>> it was previously set up? presumably without setting or changing any
> >>> modes, but simply allowing the existing frame to be updated?
> >>
> >> There's no requirement for your driver. We just want a parameter where
> >> we can conveniently disable most of DRM's drivers and reduce it to a
> >> minimum. Helps distributions to provide a simple fallback mode. Most
> >> PCI-based drivers already support that. Now we're added it to the other
> >> drivers as well.
> >>
> >>>
> >>> I think the implication is that 'firmware drivers' would mean a display
> >>> could be updated through some firmware interface, which we won't have
> >>> ... so it seems reasonable to accept that this whole driver can be
> >>> disabled in that instance.
> >>
> >> It cannot be 'mode-setted'. We get a pre-configured framebuffer from the
> >> firmware or bootloader. Whatever we draw there shows up on the screen.
> >
> > I doubt that's going to work as you expect, clocks and regulators will
> > get disabled at boot if not used by any driver.
>
> Simpledrm and simplefb attach to these firmware framebuffers. Both
> drivers look at the device tree nodes to acquire the relevant clocks and
> regulators.

How about clocks and regulators for the ancillary devices, such as
encoders, or in the R-Car case, the external composer handled by the
vsp1 driver (in drivers/media/platform/vsp1) ?

This approach may work fine on x86 desktop systems, but for ARM-based
devices, the situation is usually more complex.

> >>> Reading your mail that brought this thread up in my inbox, I think
> >>> you've already hit merge on this, so don't worry about adding a tag in
> >>> that instance, but I think this is ok.
> >>>
> >>> Reviewed-by: Kieran Bingham <[email protected]>
> >>>
> >>>> rcar_du_of_init(rcar_du_of_table);
> >>>>
> >>>> return platform_driver_register(&rcar_du_platform_driver);

--
Regards,

Laurent Pinchart

2022-01-30 23:41:43

Hi

Am 28.01.22 um 12:04 schrieb Laurent Pinchart:
> Hi Thomas,
>
> On Fri, Jan 28, 2022 at 11:46:49AM +0100, Thomas Zimmermann wrote:
>> Am 28.01.22 um 11:34 schrieb Laurent Pinchart:
>>> On Fri, Jan 28, 2022 at 10:33:21AM +0100, Thomas Zimmermann wrote:
>>>> Am 28.01.22 um 10:13 schrieb Kieran Bingham:
>>>>> Quoting Javier Martinez Canillas (2021-12-17 00:37:46)
>>>>>> According to disable Documentation/admin-guide/kernel-parameters.txt, this
>>>>>> parameter can be used to disable kernel modesetting.
>>>>>>
>>>>>> DRM drivers will not perform display-mode changes or accelerated rendering
>>>>>> and only the system framebuffer will be available if it was set-up.
>>>>>
>>>>> What is the 'system framebuffer' in this instance? Reading
>>>>> https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.txt
>>>>> it sounds like that means anything already set up by the bootloader.
>>>>
>>>> Exactly this.
>>>>
>>>>>> But only a few DRM drivers currently check for nomodeset, make this driver
>>>>>> to also support the command line parameter.
>>>>>>
>>>>>> Signed-off-by: Javier Martinez Canillas <[email protected]>
>>>>>> ---
>>>>>>
>>>>>> (no changes since v1)
>>>>>>
>>>>>> drivers/gpu/drm/rcar-du/rcar_du_drv.c | 3 +++
>>>>>> 1 file changed, 3 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_drv.c b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
>>>>>> index 5a8131ef81d5..982e450233ed 100644
>>>>>> --- a/drivers/gpu/drm/rcar-du/rcar_du_drv.c
>>>>>> +++ b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
>>>>>> @@ -701,6 +701,9 @@ static struct platform_driver rcar_du_platform_driver = {
>>>>>>
>>>>>> static int __init rcar_du_init(void)
>>>>>> {
>>>>>> + if (drm_firmware_drivers_only())
>>>>>> + return -ENODEV;
>>>>>> +
>>>>>
>>>>> This will completely disable all control of the display device when
>>>>> nomodeset is enabled.
>>>>>
>>>>> Is there any requirement for us to support outputting to the display if
>>>>> it was previously set up? presumably without setting or changing any
>>>>> modes, but simply allowing the existing frame to be updated?
>>>>
>>>> There's no requirement for your driver. We just want a parameter where
>>>> we can conveniently disable most of DRM's drivers and reduce it to a
>>>> minimum. Helps distributions to provide a simple fallback mode. Most
>>>> PCI-based drivers already support that. Now we're added it to the other
>>>> drivers as well.
>>>>
>>>>>
>>>>> I think the implication is that 'firmware drivers' would mean a display
>>>>> could be updated through some firmware interface, which we won't have
>>>>> ... so it seems reasonable to accept that this whole driver can be
>>>>> disabled in that instance.
>>>>
>>>> It cannot be 'mode-setted'. We get a pre-configured framebuffer from the
>>>> firmware or bootloader. Whatever we draw there shows up on the screen.
>>>
>>> I doubt that's going to work as you expect, clocks and regulators will
>>> get disabled at boot if not used by any driver.
>>
>> Simpledrm and simplefb attach to these firmware framebuffers. Both
>> drivers look at the device tree nodes to acquire the relevant clocks and
>> regulators.
>
> How about clocks and regulators for the ancillary devices, such as
> encoders, or in the R-Car case, the external composer handled by the
> vsp1 driver (in drivers/media/platform/vsp1) ?
>
> This approach may work fine on x86 desktop systems, but for ARM-based
> devices, the situation is usually more complex.

Well, in that case the problem has always been there. We don't make it
worse.

Best regards
Thomas

>
>>>>> Reading your mail that brought this thread up in my inbox, I think
>>>>> you've already hit merge on this, so don't worry about adding a tag in
>>>>> that instance, but I think this is ok.
>>>>>
>>>>> Reviewed-by: Kieran Bingham <[email protected]>
>>>>>
>>>>>> rcar_du_of_init(rcar_du_of_table);
>>>>>>
>>>>>> return platform_driver_register(&rcar_du_platform_driver);
>

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

Attachments:

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2022-01-31 09:27:20

by Laurent Pinchart

[permalink] [raw]

Subject: Re: [PATCH v2 31/37] drm: rcar-du: Add support for the nomodeset kernel parameter

Hi Thomas,

On Fri, Jan 28, 2022 at 12:26:03PM +0100, Thomas Zimmermann wrote:
> Am 28.01.22 um 12:04 schrieb Laurent Pinchart:
> > On Fri, Jan 28, 2022 at 11:46:49AM +0100, Thomas Zimmermann wrote:
> >> Am 28.01.22 um 11:34 schrieb Laurent Pinchart:
> >>> On Fri, Jan 28, 2022 at 10:33:21AM +0100, Thomas Zimmermann wrote:
> >>>> Am 28.01.22 um 10:13 schrieb Kieran Bingham:
> >>>>> Quoting Javier Martinez Canillas (2021-12-17 00:37:46)
> >>>>>> According to disable Documentation/admin-guide/kernel-parameters.txt, this
> >>>>>> parameter can be used to disable kernel modesetting.
> >>>>>>
> >>>>>> DRM drivers will not perform display-mode changes or accelerated rendering
> >>>>>> and only the system framebuffer will be available if it was set-up.
> >>>>>
> >>>>> What is the 'system framebuffer' in this instance? Reading
> >>>>> https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.txt
> >>>>> it sounds like that means anything already set up by the bootloader.
> >>>>
> >>>> Exactly this.
> >>>>
> >>>>>> But only a few DRM drivers currently check for nomodeset, make this driver
> >>>>>> to also support the command line parameter.
> >>>>>>
> >>>>>> Signed-off-by: Javier Martinez Canillas <[email protected]>
> >>>>>> ---
> >>>>>>
> >>>>>> (no changes since v1)
> >>>>>>
> >>>>>> drivers/gpu/drm/rcar-du/rcar_du_drv.c | 3 +++
> >>>>>> 1 file changed, 3 insertions(+)
> >>>>>>
> >>>>>> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_drv.c b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
> >>>>>> index 5a8131ef81d5..982e450233ed 100644
> >>>>>> --- a/drivers/gpu/drm/rcar-du/rcar_du_drv.c
> >>>>>> +++ b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
> >>>>>> @@ -701,6 +701,9 @@ static struct platform_driver rcar_du_platform_driver = {
> >>>>>>
> >>>>>> static int __init rcar_du_init(void)
> >>>>>> {
> >>>>>> + if (drm_firmware_drivers_only())
> >>>>>> + return -ENODEV;
> >>>>>> +
> >>>>>
> >>>>> This will completely disable all control of the display device when
> >>>>> nomodeset is enabled.
> >>>>>
> >>>>> Is there any requirement for us to support outputting to the display if
> >>>>> it was previously set up? presumably without setting or changing any
> >>>>> modes, but simply allowing the existing frame to be updated?
> >>>>
> >>>> There's no requirement for your driver. We just want a parameter where
> >>>> we can conveniently disable most of DRM's drivers and reduce it to a
> >>>> minimum. Helps distributions to provide a simple fallback mode. Most
> >>>> PCI-based drivers already support that. Now we're added it to the other
> >>>> drivers as well.
> >>>>
> >>>>>
> >>>>> I think the implication is that 'firmware drivers' would mean a display
> >>>>> could be updated through some firmware interface, which we won't have
> >>>>> ... so it seems reasonable to accept that this whole driver can be
> >>>>> disabled in that instance.
> >>>>
> >>>> It cannot be 'mode-setted'. We get a pre-configured framebuffer from the
> >>>> firmware or bootloader. Whatever we draw there shows up on the screen.
> >>>
> >>> I doubt that's going to work as you expect, clocks and regulators will
> >>> get disabled at boot if not used by any driver.
> >>
> >> Simpledrm and simplefb attach to these firmware framebuffers. Both
> >> drivers look at the device tree nodes to acquire the relevant clocks and
> >> regulators.
> >
> > How about clocks and regulators for the ancillary devices, such as
> > encoders, or in the R-Car case, the external composer handled by the
> > vsp1 driver (in drivers/media/platform/vsp1) ?
> >
> > This approach may work fine on x86 desktop systems, but for ARM-based
> > devices, the situation is usually more complex.
>
> Well, in that case the problem has always been there. We don't make it
> worse.

What's the point of adding nomodeset support in those drivers then, if
it's known not to work ?

> >>>>> Reading your mail that brought this thread up in my inbox, I think
> >>>>> you've already hit merge on this, so don't worry about adding a tag in
> >>>>> that instance, but I think this is ok.
> >>>>>
> >>>>> Reviewed-by: Kieran Bingham <[email protected]>
> >>>>>
> >>>>>> rcar_du_of_init(rcar_du_of_table);
> >>>>>>
> >>>>>> return platform_driver_register(&rcar_du_platform_driver);

--
Regards,

Laurent Pinchart

2022-01-31 10:03:15

by Thomas Zimmermann

[permalink] [raw]

Subject: Re: [PATCH v2 31/37] drm: rcar-du: Add support for the nomodeset kernel parameter

Hi

Am 28.01.22 um 12:36 schrieb Laurent Pinchart:
> Hi Thomas,
>
> On Fri, Jan 28, 2022 at 12:26:03PM +0100, Thomas Zimmermann wrote:
>> Am 28.01.22 um 12:04 schrieb Laurent Pinchart:
>>> On Fri, Jan 28, 2022 at 11:46:49AM +0100, Thomas Zimmermann wrote:
>>>> Am 28.01.22 um 11:34 schrieb Laurent Pinchart:
>>>>> On Fri, Jan 28, 2022 at 10:33:21AM +0100, Thomas Zimmermann wrote:
>>>>>> Am 28.01.22 um 10:13 schrieb Kieran Bingham:
>>>>>>> Quoting Javier Martinez Canillas (2021-12-17 00:37:46)
>>>>>>>> According to disable Documentation/admin-guide/kernel-parameters.txt, this
>>>>>>>> parameter can be used to disable kernel modesetting.
>>>>>>>>
>>>>>>>> DRM drivers will not perform display-mode changes or accelerated rendering
>>>>>>>> and only the system framebuffer will be available if it was set-up.
>>>>>>>
>>>>>>> What is the 'system framebuffer' in this instance? Reading
>>>>>>> https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.txt
>>>>>>> it sounds like that means anything already set up by the bootloader.
>>>>>>
>>>>>> Exactly this.
>>>>>>
>>>>>>>> But only a few DRM drivers currently check for nomodeset, make this driver
>>>>>>>> to also support the command line parameter.
>>>>>>>>
>>>>>>>> Signed-off-by: Javier Martinez Canillas <[email protected]>
>>>>>>>> ---
>>>>>>>>
>>>>>>>> (no changes since v1)
>>>>>>>>
>>>>>>>> drivers/gpu/drm/rcar-du/rcar_du_drv.c | 3 +++
>>>>>>>> 1 file changed, 3 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_drv.c b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
>>>>>>>> index 5a8131ef81d5..982e450233ed 100644
>>>>>>>> --- a/drivers/gpu/drm/rcar-du/rcar_du_drv.c
>>>>>>>> +++ b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
>>>>>>>> @@ -701,6 +701,9 @@ static struct platform_driver rcar_du_platform_driver = {
>>>>>>>>
>>>>>>>> static int __init rcar_du_init(void)
>>>>>>>> {
>>>>>>>> + if (drm_firmware_drivers_only())
>>>>>>>> + return -ENODEV;
>>>>>>>> +
>>>>>>>
>>>>>>> This will completely disable all control of the display device when
>>>>>>> nomodeset is enabled.
>>>>>>>
>>>>>>> Is there any requirement for us to support outputting to the display if
>>>>>>> it was previously set up? presumably without setting or changing any
>>>>>>> modes, but simply allowing the existing frame to be updated?
>>>>>>
>>>>>> There's no requirement for your driver. We just want a parameter where
>>>>>> we can conveniently disable most of DRM's drivers and reduce it to a
>>>>>> minimum. Helps distributions to provide a simple fallback mode. Most
>>>>>> PCI-based drivers already support that. Now we're added it to the other
>>>>>> drivers as well.
>>>>>>
>>>>>>>
>>>>>>> I think the implication is that 'firmware drivers' would mean a display
>>>>>>> could be updated through some firmware interface, which we won't have
>>>>>>> ... so it seems reasonable to accept that this whole driver can be
>>>>>>> disabled in that instance.
>>>>>>
>>>>>> It cannot be 'mode-setted'. We get a pre-configured framebuffer from the
>>>>>> firmware or bootloader. Whatever we draw there shows up on the screen.
>>>>>
>>>>> I doubt that's going to work as you expect, clocks and regulators will
>>>>> get disabled at boot if not used by any driver.
>>>>
>>>> Simpledrm and simplefb attach to these firmware framebuffers. Both
>>>> drivers look at the device tree nodes to acquire the relevant clocks and
>>>> regulators.
>>>
>>> How about clocks and regulators for the ancillary devices, such as
>>> encoders, or in the R-Car case, the external composer handled by the
>>> vsp1 driver (in drivers/media/platform/vsp1) ?
>>>
>>> This approach may work fine on x86 desktop systems, but for ARM-based
>>> devices, the situation is usually more complex.
>>
>> Well, in that case the problem has always been there. We don't make it
>> worse.
>
> What's the point of adding nomodeset support in those drivers then, if
> it's known not to work ?

But nomodeset is know to work: it disables the driver. The behavior is
consistent among all hardware-specific drivers.

Javier mentioned that there are kernel parameters to keep unused
clocks/regulators working.

From the distribution POV, if we have users with broken graphics
drivers we want to give them an easy workaround until we find a
solution. Passing 'nomodeset ...' on the command line gives us that.

Best regards
Thomas

>
>>>>>>> Reading your mail that brought this thread up in my inbox, I think
>>>>>>> you've already hit merge on this, so don't worry about adding a tag in
>>>>>>> that instance, but I think this is ok.
>>>>>>>
>>>>>>> Reviewed-by: Kieran Bingham <[email protected]>
>>>>>>>
>>>>>>>> rcar_du_of_init(rcar_du_of_table);
>>>>>>>>
>>>>>>>> return platform_driver_register(&rcar_du_platform_driver);
>

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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