Re: [PATCH 3/4] lib: logic_pio: Introduce MMIO_LOWER_RESERVED

[Jiaxun Yang <jiaxun.yang@flygoat.com>]

On Mon, 27 Apr 2020 12:54:06 +0100
John Garry <john.garry@huawei.com> wrote:

> On 27/04/2020 12:03, Jiaxun Yang wrote:
> > 
> > 
> > 于 2020年4月27日 GMT+08:00 下午6:43:09, John Garry
> > <john.garry@huawei.com> 写到:  
> >> On 26/04/2020 12:47, Jiaxun Yang wrote:  
> >>> That would allow platforms reserve some lower address in PIO MMIO
> >>> range to deal with legacy drivers with hardcoded I/O ports that
> >>> can't be managed by logic_pio.  
> >>
> >> Hi,
> >>
> >> Is there some reason why the logic_pio code cannot be improved to
> >> handle these devices at these "fixed" addresses? Or do you have a
> >> plan to improve it? We already support fixed bus address devices
> >> in the INDIRECT IO region.  
> > 
> > Hi,
> > 
> > The issue about "Fixed Address" is we can't control the ioport
> > That driver used to operate devices.
> > So any attempt to resolve it in logic_pio seems impossible.
> > 
> > Currently we have i8259, i8042, piix4_smbus, mc146818 rely on this
> > assumption.  
> 
> Right, and from glancing at a couple of drivers you mentioned, if we 
> were to register a logic pio region for that legacy region, there
> does not seem to be an easy place to fixup to use logic pio addresses
> (for those devices). They use hardcoded values. However if all those
> drivers were mips specific, you could fixup those drivers to use
> logic_pio addresses today through some macro. But not sure on that.
> 

Well, most of these drivers are shared with x86 so....
I guess the conversion needs two or more release cycles.

> 
> So, going back to your change, I have a dilemma wondering whether you 
> should still register a logic pio region for the legacy region
> instead of the carveout reservation, but ensure it is the first
> region registered, such that logic pio address base is 0 and no
> translation is required. At least then you have a region registered
> and it shows in /proc/ioports, but then this whole thing becomes a
> bit fragile.

Thanks for your solution. So I must register this range as early as
possible. As IRQ is the first subsystem using ISA, I'll do it before
IRQ init, just at the place I setup iormap for reserved region now.

Should be early enough to avoid any collision, as the only logic_pio
user on our system is PCI controller.

Thanks.
> 
--
Jiaxun Yang