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.
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);
--
