Re: [PATCH 1/4] ARM STM/i.MX: Allocate memory for framebuffer during probe

[Gregory CLEMENT <gregory.clement@free-electrons.com>]

On 01/04/2011 05:16 PM, Juergen Beisert wrote:
> Gregory CLEMENT wrote:
>> On 01/04/2011 03:46 PM, Juergen Beisert wrote:
>>> Gregory CLEMENT wrote:
>>>> With current code when the framebuffer is register, screen_base is not
>>>> set yet. So when we want to access framebuffer from mmap we get a
>>>> pointer to 0x0 instead of getting the pointer to the framebuffer
>>>> address. This patch fix this bug by allocating memory for framebuffer
>>>> during probe just before registering framebuffer driver.
>>>
>>> Are you sure? See below
>>
>> It was the value I get at runtime at least.
>>
>>>> Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
>>
>> [...]
>>
>>> This probe function sets up the default mode. And register_framebuffer()
>>> itself calls stmfb_activate_var() which calls stmfb_memory_mmgt(). So,
>>> when the call to register_framebuffer() returns the 'screen_base' should
>>> no longer be NULL.
>>
>> But in register_framebuffer first map_base get its value from screen_base
>> and it is only after that fb_activate_var is called. And the problem is
>> that mmap will not get screen_base but map_base and this one is set too
>> early. Extract from  register_framebuffer() in fb.c:
>>
>> 	info->cdev.dev->map_base = (unsigned long)info->screen_base;
>> map_base get its value here ------^
>> 	info->cdev.dev->size = info->cdev.size;
>>
>> 	dev = &info->dev;
>> 	dev->priv = info;
>> 	dev->id = id;
>>
>> 	sprintf(dev->name, "fb");
>>
>> 	register_device(&info->dev);
>> 	dev_add_param(dev, "enable", fb_enable_set, NULL, 0);
>> 	dev_set_param(dev, "enable", "0");
>>
>> 	if (info->num_modes && (info->mode_list != NULL) &&
>> 			(info->fbops->fb_activate_var != NULL)) {
>> 		dev_add_param(dev, "mode_name", fb_setup_mode, NULL, 0);
>> 		dev_set_param(dev, "mode_name", info->mode_list[0].name);
>> fb_activate_var is called here ------------------------^
> 
> And this call will call driver's stmfb_activate_var() (and(!) 
> stmfb_memory_mmgt()).

Yes I totally agree with this. But at this time it's too late because changing
screen_base won't change map_base. And a call to memmap is a call to
generic_memmap_rw which will return map_base.
I didn't find anywhere in video driver code a place where map_base is updated, that's
why I think that once it get its value it won't change.

> But I will check it again.
> 
> jbe
> 


-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com

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