On 06/28/2013 04:11 AM, David Herrmann wrote:
> Hi
>
> On Wed, Jun 26, 2013 at 10:49 PM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote:
>> On 06/24/2013 04:27 PM, David Herrmann wrote:
>>> The current situation regarding boot-framebuffers (VGA, VESA/VBE, EFI) on
>>> x86 causes troubles when loading multiple fbdev drivers. The global
>>> "struct screen_info" does not provide any state-tracking about which
>>> drivers use the FBs. request_mem_region() theoretically works, but
>>> unfortunately vesafb/efifb ignore it due to quirks for broken boards.
>>>
>>> Avoid this by creating a "platform-framebuffer" device with a pointer
>>> to the "struct screen_info" as platform-data. Drivers can now create
>>> platform-drivers and the driver-core will refuse multiple drivers being
>>> active simultaneously.
>>>
>>> We keep the screen_info available for backwards-compatibility. Drivers
>>> can be converted in follow-up patches.
>>>
>>> Apart from "platform-framebuffer" devices, this also introduces a
>>> compatibility option for "simple-framebuffer" drivers which recently got
>>> introduced for OF based systems. If CONFIG_X86_SYSFB is selected, we
>>> try to match the screen_info against a simple-framebuffer supported
>>> format. If we succeed, we create a "simple-framebuffer" device instead
>>> of a platform-framebuffer.
...
>>> diff --git a/arch/x86/kernel/sysfb.c b/arch/x86/kernel/sysfb.c
...
>>> +#else /* CONFIG_X86_SYSFB */
>>> +
>>> +static bool parse_mode(const struct screen_info *si,
>>> + struct simplefb_platform_data *mode)
>>> +{
>>> + return false;
>>> +}
>>> +
>>> +static int create_simplefb(const struct screen_info *si,
>>> + const struct simplefb_platform_data *mode)
>>> +{
>>> + return -EINVAL;
>>> +}
>>> +
>>> +#endif /* CONFIG_X86_SYSFB */
>>
>> Following on from my ifdef comment above, I believe those versions of
>> those functions will always cause add_sysfb() to return -ENODEV, so you
>> may as well provide a static inline for add_sysfb() instead.
>
> No. add_sysfb() is supposed to always succeed. However, if
> parse_mode/create_simplefb fail, it creates a "platform-framebuffer"
> as fallback. I don't see any way to avoid these ifdefs. Considering
> the explanation above, could you elaborate how you think this should
> work?
Ah, I wasn't getting the fallback mechanism; that if creating a simplefb
wasn't possible or didn't succeed, a platformfb device would be created
instead.
Perhaps the following might be slightly clearer; there are certainly
fewer nesting levels:
static __init int add_sysfb(void)
{
const struct screen_info *si = &screen_info;
struct simplefb_platform_data mode;
struct platform_device *pd;
bool compatible = false;
int ret;
compatible = parse_mode(si, &mode);
if (compatible) {
ret = create_simplefb(si, &mode);
if (!ret)
return 0;
}
pd = platform_device_register_resndata(NULL,
"platform-framebuffer", 0,
NULL, 0, si, sizeof(*si));
ret = IS_ERR(pd) ? PTR_ERR(pd) : 0;
return ret;
}
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