On Wed, Sep 27, 2023 at 7:10 PM Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
Hi Jim,
thanks for your patch!
On Tue, Sep 26, 2023 at 7:52 PM Jim Quinlan <james.quinlan@xxxxxxxxxxxx> wrote:
Without this commit, the use of dma_alloc_coherent() while
using CONFIG_DMA_RESTRICTED_POOL=y breaks devices from working.
For example, the common Wifi 7260 chip (iwlwifi) works fine
on arm64 with restricted memory but not on arm, unless this
commit is applied.
Signed-off-by: Jim Quinlan <james.quinlan@xxxxxxxxxxxx>
(...)
+ select DMA_DIRECT_REMAP
Christoph invented that symbol so he can certainly
explain what is missing to use this on ARM.
This looks weird to me, because:
git grep atomic_pool_initarch/arm/mm/dma-mapping.c:static int __init atomic_pool_init(void)
kernel/dma/pool.c:static int __init dma_atomic_pool_init(void)
Now you have two atomic DMA pools in the kernel,
and a lot more than that is duplicated. I'm amazed that it
compiles at all.
Clearly if you want to do this, surely the ARM-specific
arch/arm/mm/dma-mapping.c and arch/arm/mm/dma-mapping-nommu.c
needs to be removed at the same time?
However I don't think it's that simple, because Christoph would surely
had done this a long time ago if it was that simple.
Hello Linus,
Yes, this is the reason I used "RFC" as the fix looked too easy to be viable :-)
I debugged it enough to see that the host driver's
writes to the dma_alloc_coherent() region were not appearing in
memory, and that
led me to DMA_DIRECT_REMAP.