linux-kernel - Re: [PATCH 4/8] fbdev: ssd1307fb: Use vmalloc to allocate video memory.

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Date:	Sat, 7 Feb 2015 12:18:21 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	niederp@...sik.uni-kl.de
Cc:	linux-fbdev@...r.kernel.org, plagnioj@...osoft.com,
	tomi.valkeinen@...com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] fbdev: ssd1307fb: Use vmalloc to allocate video
 memory.

Hi,

On Fri, Feb 06, 2015 at 11:28:10PM +0100, niederp@...sik.uni-kl.de wrote:
> From: Thomas Niederprüm <niederp@...sik.uni-kl.de>
> 
> It makes sense to use vmalloc to allocate the video buffer since it
> has to be page aligned memory for using it with mmap.

Please wrap your commit log at 80 chars.

It looks like there's numerous fbdev drivers using this (especially
since you copy pasted that code, without mentionning it).

That should be turned into an allocator so that drivers all get this
right.

> Also deffered io seems buggy in combination with kmalloc'ed memory
> (crash on unloading the module).

And maybe that's the real issue to fix.

> Signed-off-by: Thomas Niederprüm <niederp@...sik.uni-kl.de>
> ---
>  drivers/video/fbdev/ssd1307fb.c | 43 +++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 41 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/video/fbdev/ssd1307fb.c b/drivers/video/fbdev/ssd1307fb.c
> index 01cfb46..945ded9 100644
> --- a/drivers/video/fbdev/ssd1307fb.c
> +++ b/drivers/video/fbdev/ssd1307fb.c
> @@ -11,6 +11,7 @@
>  #include <linux/i2c.h>
>  #include <linux/fb.h>
>  #include <linux/uaccess.h>
> +#include <linux/vmalloc.h>
>  #include <linux/of_device.h>
>  #include <linux/of_gpio.h>
>  #include <linux/pwm.h>
> @@ -93,6 +94,43 @@ static struct fb_var_screeninfo ssd1307fb_var = {
>  	.bits_per_pixel	= 1,
>  };
>  
> +static void *rvmalloc(unsigned long size)
> +{
> +	void *mem;
> +	unsigned long adr;
> +
> +	size = PAGE_ALIGN(size);

Isn't vmalloc already taking care of that?

> +	mem = vmalloc_32(size);

Why the 32 bits variant?

> +	if (!mem)
> +		return NULL;
> +
> +	memset(mem, 0, size); /* Clear the ram out, no junk to the user */
> +	adr = (unsigned long) mem;
> +	while (size > 0) {
> +		SetPageReserved(vmalloc_to_page((void *)adr));

I'm not really sure it makes sense to mark all pages reserved if we're
not even sure we're going to use mmap.

And why do you need to mark these pages reserved in the first place?

> +		adr += PAGE_SIZE;
> +		size -= PAGE_SIZE;
> +	}
> +
> +	return mem;
> +}
> +
> +static void rvfree(void *mem, unsigned long size)
> +{
> +	unsigned long adr;
> +
> +	if (!mem)
> +		return;
> +
> +	adr = (unsigned long) mem;
> +	while ((long) size > 0) {
> +		ClearPageReserved(vmalloc_to_page((void *)adr));
> +		adr += PAGE_SIZE;
> +		size -= PAGE_SIZE;
> +	}
> +	vfree(mem);
> +}
> +
>  static struct ssd1307fb_array *ssd1307fb_alloc_array(u32 len, u8 type)
>  {
>  	struct ssd1307fb_array *array;
> @@ -538,13 +576,13 @@ static int ssd1307fb_probe(struct i2c_client *client,
>  	if (of_property_read_u32(node, "solomon,vcomh", &par->vcomh))
>  		par->vcomh = par->device_info->default_vcomh;
>  
> -	vmem = devm_kzalloc(&client->dev, vmem_size, GFP_KERNEL);
>  	if (of_property_read_u32(node, "solomon,dclk-div", &par->dclk_div))
>  		par->dclk_div = par->device_info->default_dclk_div;
>  
>  	if (of_property_read_u32(node, "solomon,dclk-frq", &par->dclk_frq))
>  		par->dclk_frq  = par->device_info->default_dclk_frq;
>  
> +	vmem = rvmalloc(vmem_size);
>  	if (!vmem) {
>  		dev_err(&client->dev, "Couldn't allocate graphical memory.\n");
>  		ret = -ENOMEM;
> @@ -570,7 +608,7 @@ static int ssd1307fb_probe(struct i2c_client *client,
>  	info->var.blue.offset = 0;
>  
>  	info->screen_base = (u8 __force __iomem *)vmem;
> -	info->fix.smem_start = (unsigned long)vmem;
> +	info->fix.smem_start = __pa(vmem);

Why are you changing from virtual to physical address here?

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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