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 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 ------------------------^


This code is new for me, maybe I missed something.

> 
> 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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