Messages in this thread | | | From | Arnd Bergmann <> | Date | Tue, 28 Jun 2022 09:08:14 +0200 | Subject | Re: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO_BUS |
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On Tue, Jun 28, 2022 at 5:25 AM Michael Schmitz <schmitzmic@gmail.com> wrote: > Am 28.06.2022 um 09:12 schrieb Michael Schmitz: > > Leaving the bounce buffer handling in place, and taking a few other > liberties - this is what converting the easiest case (a3000 SCSI) might > look like. Any obvious mistakes? The mvme147 driver would be very > similar to handle (after conversion to a platform device). > > The driver allocates bounce buffers using kmalloc if it hits an > unaligned data buffer - can such buffers still even happen these days? > If I understand dma_map_single() correctly, the resulting dma handle > would be equally misaligned? > > To allocate a bounce buffer, would it be OK to use dma_alloc_coherent() > even though AFAIU memory used for DMA buffers generally isn't consistent > on m68k?
I think it makes sense to skip the bounce buffering as you do here: the only standardized way we have for integrating that part is to use the swiotlb infrastructure, but as you mentioned earlier that part is probably too resource-heavy here for Amiga.
I see two other problems with your patch though:
a) you still duplicate the cache handling: the cache_clear()/cache_push() is supposed to already be done by dma_map_single() when the device is not cache-coherent.
b) The bounce buffer is never mapped here, instead you have the virt_to_phys() here, which is not the same. I think you need to map the pointer that actually gets passed down to the device after deciding to use a bouce buffer or not.
Arnd
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