Messages in this thread | | | Date | Wed, 29 Jun 2022 09:03:37 +1200 | Subject | Re: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO_BUS | From | Michael Schmitz <> |
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Hi Geert,
On 28/06/22 19:03, Geert Uytterhoeven wrote: > >> 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). > Thanks, looks reasonable. Thanks, I'll take care of Arnd's comments and post a corrected version later. >> The driver allocates bounce buffers using kmalloc if it hits an >> unaligned data buffer - can such buffers still even happen these days? > No idea. Hmmm - I think I'll stick a WARN_ONCE() in there so we know whether this code path is still being used. > >> 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? >> >> Thinking ahead to the other two Amiga drivers - I wonder whether >> allocating a static bounce buffer or a DMA pool at driver init is likely >> to succeed if the kernel runs from the low 16 MB RAM chunk? It certainly >> won't succeed if the kernel runs from a higher memory address, so the >> present bounce buffer logic around amiga_chip_alloc() might still need >> to be used here. >> >> Leaves the question whether converting the gvp11 and a2091 drivers is >> actually worth it, if bounce buffers still have to be handled explicitly. > A2091 should be straight-forward, as A3000 is basically A2091 on the > motherboard (comparing the two drivers, looks like someone's been > sprinkling mb()s over the A3000 driver).
Yep, and at least the ones in the dma_setup() function are there for no reason (the compiler won't reorder stores around the cache flush calls, I hope?).
Just leaves the 24 bit DMA mask there (and likely need for bounce buffers).
> I don't have any of these SCSI host adapters (not counting the A590 > (~A2091) expansion of the old A500, which is not Linux-capable, and > hasn't been powered on for 20 years).
I wonder whether kullervo has survived - that one was an A3000. Should have gone to Adrian a few years ago...
Cheers,
Michael
> > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds
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