(2010/08/17 13:15), Huang Ying wrote:
> On Tue, 2010-08-17 at 10:43 +0800, Jin Dongming wrote:
>> (2010/08/17 10:37), Huang Ying wrote:
>>> On Tue, 2010-08-17 at 08:56 +0800, 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 whether I/O remapping is successful or not, the function returns
>>>> NULL always.
>>>
>>> No. NULL is returned for error path only. Please check the code again.
>>
>> There three places used the local variable vaddr in acpi_pre_map() in next-tree.
>> 1. 115 vaddr = __acpi_try_ioremap(paddr, size);
>> 2. 122 vaddr = ioremap(pg_off, pg_sz);
>> 3. 135 vaddr = __acpi_try_ioremap(paddr, size);
>>
>> Let's think about the following statement.
>> Assumption: the physical address has never been remapped.
>> Step:
>> 1. vaddr == NULL
>> Because the physical address is not registered in the acpi_iomaps,
>> it should be returned NULL from __acpi_try_ioremap().
>>
>> 2. vaddr == the virtual address of the physical address.
>> Here if ioremap is successful, the value of vaddr should be
>> the virtual address returned from ioremap().
>>
>> 3. vaddr == NULL <== IMPORTANT
>> Here it is because the physical address has not been registered
>> in the acpi_iomaps yet, it still return NULL from __acpi_try_ioremap().
>> So it is why vaddr == NULL, even if the physical address has never
>> been remapped.
>>
>> Result: vaddr == NULL.
>
> return vaddr + (paddr - pg_off), is not NULL for common cases.
>
>> And if the vaddr is not NULL, it could not be added into acpi_iomaps.
>> Codes in acpi_pre_map() is like following.
>>
>> 134 spin_lock_irqsave(&acpi_iomaps_lock, flags);
>> 135 vaddr = __acpi_try_ioremap(paddr, size); <== the 3rd step
>> 136 if (vaddr) {
>> 137 spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
>> 138 iounmap(map->vaddr);
>> 139 kfree(map);
>> 140 return vaddr;
>> 141 }
>> 142 list_add_tail_rcu(&map->list, &acpi_iomaps); <== add into acpi_iomaps.
>> 143 spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
>
> Oops, this is a bug, and your patch really fix it. But I think you
> should change the patch description. NULL is not returned in almost all
> cases. Because (paddr - pg_off) is not zero in common cases.
>
> Best Regards,
> Huang Ying
>
OK. I will modify the description of this patch and resend it.
Best Regards,
Jin Dongming
>
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