[v3] mtd: mtdchar: allow mmap for ram devices in memory address space.

use mtd_get_unmapped_area, as asked by an ancient comment, to get
the physical address (if any) in memory of the mtd device.

Therefore, mapram_unmapped_area had to be changed to return the physical
address, not the virtual one, For the NOMMU case, that makes no difference,
but for the MMU case, it is needed by mapram_unmapped_area to implement mmap.

Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Cc: David Howells <dhowells@redhat.com>
Cc: Markus Niebel <Markus.Niebel@tqs.de>
Cc: Brian Norris <computersforpeace@gmail.com>
---
v3: avoid duplicating test done by mtd_get_unmapped_area

 drivers/mtd/chips/map_ram.c |    2 +-
 drivers/mtd/mtdchar.c       |   24 ++++++++++--------------
 2 files changed, 11 insertions(+), 15 deletions(-)

In case this gets resurrected...

On Fri, Mar 07, 2014 at 02:54:39PM +0100, Philippe De Muyter wrote:
> use mtd_get_unmapped_area, as asked by an ancient comment, to get
> the physical address (if any) in memory of the mtd device.
> 
> Therefore, mapram_unmapped_area had to be changed to return the physical
> address, not the virtual one, For the NOMMU case, that makes no difference,
> but for the MMU case, it is needed by mapram_unmapped_area to implement mmap.
> 
> Signed-off-by: Philippe De Muyter <phdm@macqel.be>
> Cc: David Howells <dhowells@redhat.com>
> Cc: Markus Niebel <Markus.Niebel@tqs.de>
> Cc: Brian Norris <computersforpeace@gmail.com>
> ---
> v3: avoid duplicating test done by mtd_get_unmapped_area
> 
>  drivers/mtd/chips/map_ram.c |    2 +-
>  drivers/mtd/mtdchar.c       |   24 ++++++++++--------------
>  2 files changed, 11 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/mtd/chips/map_ram.c b/drivers/mtd/chips/map_ram.c
> index 991c2a1..e93d147 100644
> --- a/drivers/mtd/chips/map_ram.c
> +++ b/drivers/mtd/chips/map_ram.c
> @@ -92,7 +92,7 @@ static unsigned long mapram_unmapped_area(struct mtd_info *mtd,
>  					  unsigned long flags)
>  {
>  	struct map_info *map = mtd->priv;
> -	return (unsigned long) map->virt + offset;
> +	return (unsigned long) map->phys + offset;
>  }
>  
>  static int mapram_read (struct mtd_info *mtd, loff_t from, size_t len, size_t *retlen, u_char *buf)
> diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
> index 2147e73..5956246 100644
> --- a/drivers/mtd/mtdchar.c
> +++ b/drivers/mtd/mtdchar.c
> @@ -1112,20 +1112,16 @@ static int mtdchar_mmap(struct file *file, struct vm_area_struct *vma)
>  #ifdef CONFIG_MMU
>  	struct mtd_file_info *mfi = file->private_data;
>  	struct mtd_info *mtd = mfi->mtd;
> -	struct map_info *map = mtd->priv;
> -
> -        /* This is broken because it assumes the MTD device is map-based
> -	   and that mtd->priv is a valid struct map_info.  It should be
> -	   replaced with something that uses the mtd_get_unmapped_area()
> -	   operation properly. */
> -	if (0 /*mtd->type == MTD_RAM || mtd->type == MTD_ROM*/) {
> -#ifdef pgprot_noncached
> -		if (file->f_flags & O_DSYNC || map->phys >= __pa(high_memory))
> -			vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> -#endif
> -		return vm_iomap_memory(vma, map->phys, map->size);
> -	}
> -	return -ENODEV;
> +	loff_t offset = vma->vm_pgoff << PAGE_SHIFT;
> +	loff_t len = vma->vm_end - vma->vm_start;
> +	phys_addr_t start;
> +
> +	start = mtd_get_unmapped_area(mtd, len, offset, vma->vm_flags);

Hmm, you're storing an 'unsigned long' in 'phys_addr_t', then treating
it as unsigned for the error checking. Is that guaranteed to work right?
Especially if sizeof(phys_addr_t) != sizeof(unsigned long)? e.g., if
phys_addr_t is 64 bits (with PAE?), but unsigned long is 32-bits, we
might see:

	start = mtd_get_unmapped_area(); // -EOPNOTSUPP

But -EOPNOTSUPP in a 32-bit unsigned long is only:

	0xffffffa1

which extends to:

	0x00000000ffffffa1

and doesn't match favorably with '-EOPNOTSUPP' when you compare it
later.

I think it makes more sense for 'start' to either match the return type
of mtd_get_unmapped_area() (i.e., unsigned long), or else just be a
signed type, so we don't have the unsigned/signed comparison issues
below.

Regards,
Brian

> +	if (start == -EOPNOTSUPP)
> +		return -ENODEV;
> +	if (start == -EINVAL)
> +		return -EINVAL;
> +	return vm_iomap_memory(vma, start, len);
>  #else
>  	return vma->vm_flags & VM_SHARED ? 0 : -EACCES;
>  #endif
> -- 
> 1.7.5.3
>