Quoting Will Deacon (2019-07-10 07:14:34)
> On Fri, Jun 14, 2019 at 01:37:15PM -0700, Stephen Boyd wrote:
> > @@ -84,7 +91,10 @@ void *memremap(resource_size_t offset, size_t size, unsigned long flags)
> > }
> >
> > /* Try all mapping types requested until one returns non-NULL */
> > - if (flags & MEMREMAP_WB) {
> > + if ((flags & MEMREMAP_RO) && is_ram != REGION_INTERSECTS)
> > + addr = arch_memremap_ro(offset, size);
> > +
> > + if (!addr && (flags & MEMREMAP_WB)) {
> > /*
> > * MEMREMAP_WB is special in that it can be satisfied
> > * from the direct map. Some archs depend on the
> > @@ -103,7 +113,8 @@ void *memremap(resource_size_t offset, size_t size, unsigned long flags)
> > * address mapping. Enforce that this mapping is not aliasing
> > * System RAM.
> > */
> > - if (!addr && is_ram == REGION_INTERSECTS && flags != MEMREMAP_WB) {
> > + if (!addr && is_ram == REGION_INTERSECTS &&
> > + (flags != MEMREMAP_WB || flags != MEMREMAP_RO)) {
> > WARN_ONCE(1, "memremap attempted on ram %pa size: %#lx\n",
> > &offset, (unsigned long) size);
> > return NULL;
>
> This function seems a little confused about whether 'flags' is really a
> bitmap of flags, or whether it is equal to exactly one entry in the enum.
> Given that I think it's sensible for somebody to specify 'MEMREMAP_RO |
> MEMREMAP_WT', then we probably need to start checking these things a bit
> more thoroughly so we can reject unsupported combinations at the very least.
>
I'm also confused about the same thing. I thought it was a "getting
worse via best effort" type of thing based on the comment above the
function.
* In the case of multiple flags, the different
* mapping types will be attempted in the order listed below until one of
* them succeeds.
(I now realize I should have documented the new flag so that this order
would be known. I'll resend this series again with the documentation
fix.)
I also thought that the combination of read-only and write through would
be OK because the flags are more of a best effort approach to making a
mapping. Given that, is there anything to reject? Or do we just keep
trying until we can't try anymore?
