Hi Michael,

On Tue, Jun 28, 2022 at 5:26 AM Michael Schmitz [off-list ref] wrote:

Am 28.06.2022 um 09:12 schrieb Michael Schmitz:

quoted

On 27/06/22 20:26, Geert Uytterhoeven wrote:

quoted

On Sat, Jun 18, 2022 at 3:06 AM Michael Schmitz [off-list ref]
wrote:

quoted

Am 18.06.2022 um 00:57 schrieb Arnd Bergmann:

quoted

From: Arnd Bergmann <arnd@arndb.de>

All architecture-independent users of virt_to_bus() and bus_to_virt()
have been fixed to use the dma mapping interfaces or have been
removed now.  This means the definitions on most architectures, and the
CONFIG_VIRT_TO_BUS symbol are now obsolete and can be removed.

The only exceptions to this are a few network and scsi drivers for m68k
Amiga and VME machines and ppc32 Macintosh. These drivers work
correctly
with the old interfaces and are probably not worth changing.

The Amiga SCSI drivers are all old WD33C93 ones, and replacing
virt_to_bus by virt_to_phys in the dma_setup() function there would
cause no functional change at all.

FTR, the sgiwd93 driver use dma_map_single().

Thanks! From what I see, it doesn't have to deal with bounce buffers
though?

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.

The driver allocates bounce buffers using kmalloc if it hits an
unaligned data buffer - can such buffers still even happen these days?

No idea.

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).

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).

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