Re: [v5.4 stable] arm: stm32: Regression observed on "no-map" reserved memory region

[Alexandre TORGUE]

Hi Quentin,

On 5/10/21 12:09 PM, Quentin Perret wrote:
> Hi Alexandre,
>
> On Friday 07 May 2021 at 17:15:20 (+0200), Alexandre TORGUE wrote:
> > Did you get time to continue some tests on this issue ?
>
> I did try a few things, but still fail to reproduced :/
>
> > On my side this DT is not working:
> >
> > memory@c0000000 {
> >          reg = <0xc0000000 0x20000000>;
> > };
> >
> > reserved-memory {
> >          #address-cells = <1>;
> >          #size-cells = <1>;
> >          ranges;
> >
> >          gpu_reserved: gpu@d4000000 {
> >                  reg = <0xd4000000 0x4000000>;
> >                  no-map;
> >          };
> > };
>
> So this does change how memory appears in /proc/iomem for me switching
> from 5.4.101 to v5.4.102 -- for the former d4000000-d7ffffff doesn't
> appear at all, and for the latter it appears as 'reserved'.
>
> But still, it never gets accounted as System RAM for me ...
>
> > Let me know if I can help.
>
> Could you please confirm you get a correct behaviour with 5.10.31 like
> Florian? If so, then bisecting to figure out what we're missing in older
> LTSes would help, but again it feels like we should just revert -- this
> wasn't really a fix in the first place.


We saw that patches [1] and [2] cause issue on stable version (at least 
for 5.4). As you said issue can be seen with above device tree and check 
in /proc/iomem than gpu_reserved region is taken by the kernel as 
"System RAM".

On v5.10 stream there are no issues seen taking patches [1]&[2] and the 
reason is linked to patches [3]&[4] which have been introduced in 
v5.10.0. Reverting them give me the same behavior than on stable version.


[1] of/fdt: Make sure no-map does not remove already reserved regions
[2] fdt: Properly handle "no-map" field in the memory region
[3] arch, drivers: replace for_each_membock() with for_each_mem_range()
[4] memblock: use separate iterators for memory and reserved regions

regards
Alex

> Thanks,
> Quentin