On Thursday, September 02, 2010 01:20:18 am Jin Dongming wrote:
> acpi_pre_map() is used for remapping the physical address of I/O, so
> it should be return NULL or remapped virtual address. The problem is
> that when (paddr - pg_off) equals 0, no matter whether I/O remapping is
> successful or not, the function returns NULL.
>
> In acpi_pre_map(), after the physical address is remapped successfully,
> it will check whether the physical address has been added into acpi_iomaps
> list again.
> - If the physical address has been added into acpi_iomaps, the virtual
> address will be saved in vaddr.
> - Otherwise, NULL be saved in vaddr.
>
> So if the physical address is the first time to be remapped, vaddr will be
> NULL always.
>
> In many cases, (paddr - pg_off) may not equal 0. So the function could work
> well. In our machine, (paddr - pg_off) equals 0, so the return value of
> acpi_pre_map() is NULL.
>
> This patch fixed it and I confirmed it on x86_64 next-tree.
This description is complicated and obscures the very simple bug
you are fixing. I suggest something like this:
ACPI: fix acpi_pre_map() return value
After we ioremap() a new region, we call __acpi_try_ioremap() to
see whether another thread has already mapped the same region.
This check clobbers "vaddr", so compute the return value using
the ioremap() result "map->vaddr" instead.
> v2:
> Modified the unsuitable description of patch.
>
> v3:
> Modified the wrong words in the description of patch.
>
> Signed-off-by: Jin Dongming <jin.dongming@xxxxxxxxxxxxxxxxxx>
> Acked-by: Huang Ying <ying.huang@xxxxxxxxx>
> ---
> drivers/acpi/atomicio.c | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/atomicio.c b/drivers/acpi/atomicio.c
> index 8f8bd73..1bc2614 100644
> --- a/drivers/acpi/atomicio.c
> +++ b/drivers/acpi/atomicio.c
> @@ -133,7 +133,7 @@ static void __iomem *acpi_pre_map(phys_addr_t paddr,
>
> spin_lock_irqsave(&acpi_iomaps_lock, flags);
> vaddr = __acpi_try_ioremap(paddr, size);
> - if (vaddr) {
> + if (unlikely(vaddr)) {
This "unlikely" addition also obscures things. It's completely
unrelated to the bug you're fixing, so it should be in a different
patch, and I'm dubious that there's enough performance advantage to
compensate for the decreased code readability. I wouldn't make this
change unless you can measure a performance improvement.
> spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
> iounmap(map->vaddr);
> kfree(map);
> @@ -142,7 +142,7 @@ static void __iomem *acpi_pre_map(phys_addr_t paddr,
> list_add_tail_rcu(&map->list, &acpi_iomaps);
> spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
>
> - return vaddr + (paddr - pg_off);
> + return map->vaddr + (paddr - pg_off);
Since you're changing this line anyway, I think you should change it to:
return map->vaddr + (paddr - map->paddr);
so it matches __acpi_try_ioremap().
> err_unmap:
> iounmap(vaddr);
> return NULL;
> -- 1.7.1.
>
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