Hi Finn,
On Mon, Jun 3, 2019 at 1:32 AM Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx> wrote:
> On Sun, 2 Jun 2019, Geert Uytterhoeven wrote:
> > On Sun, Jun 2, 2019 at 3:29 AM Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>
> > wrote:
> > > A system bus error during a PDMA transfer can mess up the calculation
> > > of the transfer residual (the PDMA handshaking hardware lacks a byte
> > > counter). This results in data corruption.
> > >
> > > The algorithm in this patch anticipates a bus error by starting each
> > > transfer with a MOVE.B instruction. If a bus error is caught the
> > > transfer will be retried. If a bus error is caught later in the
> > > transfer (for a MOVE.W instruction) the transfer gets failed and
> > > subsequent requests for that target will use PIO instead of PDMA.
> > >
> > > This avoids the "!REQ and !ACK" error so the severity level of that
> > > message is reduced to KERN_DEBUG.
> > >
> > > Cc: Michael Schmitz <schmitzmic@xxxxxxxxx>
> > > Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> > > Cc: stable@xxxxxxxxxxxxxxx # v4.14+
> > > Fixes: 3a0f64bfa907 ("mac_scsi: Fix pseudo DMA implementation")
> > > Reported-by: Chris Jones <chris@xxxxxxxxxxxxxxxx>
> > > Tested-by: Stan Johnson <userm57@xxxxxxxxx>
> > > Signed-off-by: Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>
> >
> > Thanks for your patch!
> >
> > > ---
> > > arch/m68k/include/asm/mac_pdma.h | 179 +++++++++++++++++++++++++++
> > > drivers/scsi/mac_scsi.c | 201 ++++++++-----------------------
> >
> > Why have you moved the PDMA implementation to a header file under
> > arch/m68k/? Do you intend to reuse it by other drivers?
> >
>
> There are a couple of reasons: the mac_esp driver also uses PDMA and the
> NuBus PowerMac port also uses mac_scsi.c. OTOH, the NuBus PowerMac port is
> still out-of-tree, and it is unclear whether the mac_esp driver will ever
> benefit from this code.
So you do have future sharing in mind...
> > If not, please keep it in the driver, so (a) you don't need an ack from
> > me ;-), and (b) your change may be easier to review.
>
> I take your wink to mean that you don't want to ask the SCSI maintainers
> to review m68k asm. Putting aside the code review process for a moment, do
I meant that apart from the code containing m68k assembler source, it
is not related to arch/m68k/, and thus belongs to the driver.
There are several other drivers that contain pieces of assembler code.
> you have an opinion on the most logical way to organise this sort of code,
> from the point-of-view of maintainability, re-usability, readability etc.?
If the code is used by multiple SCSI drivers, you can move it to a header
file under drivers/scsi/.
If the code is shared by drivers belonging to multiple subsystems, you can
move it to a header file under include/linux/.
Anyone who has a better solution?
Thanks!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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
