Re: [PATCH 1/2] of: Create platform devices for OF framebuffers

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 13.04.22 um 14:51 schrieb Rob Herring:
> On Wed, Apr 13, 2022 at 4:24 AM Thomas Zimmermann <tzimmermann@suse.de> wrote:
>>
>> Create a platform device for each OF-declared framebuffer and have
>> offb bind to these devices. Allows for real hot-unplugging and other
>> drivers besides offb.
>>
>> Originally, offb created framebuffer devices while initializing its
>> module by parsing the OF device tree. No actual Linux device was set
>> up. This tied OF framebuffers to offb and makes writing other drivers
>> for the OF framebuffers complicated. The absence of a Linux device
>> prevented real hot-unplugging. Adding a distinct platform device for
>> each OF framebuffer solves both problems. Specifically, a DRM drivers
>> can now provide graphics output with modern userspace.
>>
>> Some of the offb init code is now located in the OF initialization.
>> There's now also an implementation of of_platform_default_populate_init(),
>> which was missing before. The OF side creates different devices for
>> either OF display nodes or bootx displays as they require different
>> handling by the driver. The offb drivers picks up each type of device
>> and runs the appropriate fbdev initialization.
>>
>> Tested with OF display nodes on qemu's ppc64le target.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>> ---
>>   drivers/of/platform.c      | 73 ++++++++++++++++++++++++++--
>>   drivers/video/fbdev/offb.c | 98 +++++++++++++++++++++++++-------------
>>   2 files changed, 134 insertions(+), 37 deletions(-)
>>
>> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
>> index a16b74f32aa9..4c63b9a73587 100644
>> --- a/drivers/of/platform.c
>> +++ b/drivers/of/platform.c
>> @@ -447,6 +447,60 @@ int of_platform_bus_probe(struct device_node *root,
>>   }
>>   EXPORT_SYMBOL(of_platform_bus_probe);
>>
>> +static int __init of_platform_populate_framebuffers(void)
>> +{
>> +       struct device_node *boot_display = NULL;
>> +       struct device_node *node;
>> +       struct platform_device *dev;
>> +       int ret;
>> +
>> +       node = of_get_compatible_child(of_chosen, "simple-framebuffer");
>> +       of_platform_device_create(node, NULL, NULL);
>> +       of_node_put(node);
>> +
> 
> The rest is PPC only, so bail out here if !PPC.
> 
>> +       /* Check if we have a MacOS display without a node spec */
>> +       if (of_get_property(of_chosen, "linux,bootx-noscreen", NULL)) {
>> +               /*
>> +                * The old code tried to work out which node was the MacOS
>> +                * display based on the address. I'm dropping that since the
>> +                * lack of a node spec only happens with old BootX versions
>> +                * (users can update) and with this code, they'll still get
>> +                * a display (just not the palette hacks).
>> +                */
>> +               dev = platform_device_alloc("bootx-noscreen", 0);
>> +               if (WARN_ON(!dev))
>> +                       return -ENOMEM;
>> +               ret = platform_device_add(dev);
>> +               if (WARN_ON(ret)) {
>> +                       platform_device_put(dev);
>> +                       return ret;
>> +               }
>> +       }
>> +
>> +       /*
>> +        * For OF framebuffers, first create the device for the boot display,
>> +        * then for the other framebuffers. Only fail for the boot display;
>> +        * ignore errors for the rest.
>> +        */
>> +       for_each_node_by_type(node, "display") {
>> +               if (!of_get_property(node, "linux,opened", NULL) ||
>> +                   !of_get_property(node, "linux,boot-display", NULL))
>> +                       continue;
>> +               dev = of_platform_device_create(node, "of-display", NULL);
>> +               if (WARN_ON(!dev))
>> +                       return -ENOMEM;
>> +               boot_display = node;
>> +               break;
>> +       }
>> +       for_each_node_by_type(node, "display") {
>> +               if (!of_get_property(node, "linux,opened", NULL) || node == boot_display)
>> +                       continue;
>> +               of_platform_device_create(node, "of-display", NULL);
>> +       }
>> +
>> +       return 0;
>> +}
>> +
>>   /**
>>    * of_platform_populate() - Populate platform_devices from device tree data
>>    * @root: parent of the first level to probe or NULL for the root of the tree
>> @@ -541,9 +595,7 @@ static int __init of_platform_default_populate_init(void)
>>                  of_node_put(node);
>>          }
>>
>> -       node = of_get_compatible_child(of_chosen, "simple-framebuffer");
>> -       of_platform_device_create(node, NULL, NULL);
>> -       of_node_put(node);
>> +       of_platform_populate_framebuffers();
>>
>>          /* Populate everything else. */
>>          of_platform_default_populate(NULL, NULL, NULL);
> 
> I'm pretty sure it's just this call that's the problem for PPC though
> none of the above existed when adding this caused a regression. Can we
> remove the ifdef and just make this call conditional on
> !IS_ENABLED(CONFIG_PPC).

Together with the changes in of_platform_populate_framebuffers(), the 
code is more or less an "if-else" depending on PPC. I'll drop 
of_platform_populate_framebuffers() from the patch and make a separate 
implementation of of_platform_default_populate_init for PPC. Seems like 
the easiest solution to me.

Best regards
Thomas

> 
> 
>> @@ -551,6 +603,20 @@ static int __init of_platform_default_populate_init(void)
>>          return 0;
>>   }
>>   arch_initcall_sync(of_platform_default_populate_init);
>> +#else
>> +static int __init of_platform_default_populate_init(void)
>> +{
>> +       device_links_supplier_sync_state_pause();
>> +
>> +       if (!of_have_populated_dt())
>> +               return -ENODEV;
>> +
>> +       of_platform_populate_framebuffers();
>> +
>> +       return 0;
>> +}
>> +arch_initcall_sync(of_platform_default_populate_init);
>> +#endif
>>
>>   static int __init of_platform_sync_state_init(void)
>>   {
>> @@ -558,7 +624,6 @@ static int __init of_platform_sync_state_init(void)
>>          return 0;
>>   }
>>   late_initcall_sync(of_platform_sync_state_init);
>> -#endif
>>
>>   int of_platform_device_destroy(struct device *dev, void *data)
>>   {

-- 
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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