Re: [PATCH v3 5/6] MIPS: implement architecture-specific 'pci_remap_iospace()'

[Arnd Bergmann]

On Thu, Dec 16, 2021 at 3:27 PM Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx> wrote:
> 在 2021/12/16 14:18, Arnd Bergmann 写道:
> >> It got refactored by this patch as TLB entries are expensive on MIPS,
> >> also the size of IO range doesn't always fits a page.
> > Are PIO accesses common enough that the TLB entry makes a difference?
> > I would imagine that on most systems with a PCI bus, there is not even
> > a single device that exposes an I/O resource, and even on those devices that
> > do, the kernel drivers tend to pick MMIO whenever both are available.
>
> Actually that was claimed by the author of this patch :-)
> I can understand the point. As he is working on a ramips system utlizes
> 1004Kec,
> which has only 32 TLB entries, saving a entry can give considerable
> improvement.

Ok

> For Loongson as we have legacy i8042/i8259 which can only be accessed via
> PIO, the access is very common.

Ah, right. It makes a lot of sense that anything based on ISA PC peripherals
would need it, regardless of the PCI support.

       Arnd