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Date: Mon, 3 Jun 2019 09:32:36 +1000 (AEST) From: Finn Thain <fthain@...egraphics.com.au> To: Geert Uytterhoeven <geert@...ux-m68k.org> cc: "James E.J. Bottomley" <jejb@...ux.ibm.com>, "Martin K. Petersen" <martin.petersen@...cle.com>, Michael Schmitz <schmitzmic@...il.com>, scsi <linux-scsi@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, stable <stable@...r.kernel.org>, linux-m68k <linux-m68k@...ts.linux-m68k.org> Subject: Re: [PATCH 5/7] scsi: mac_scsi: Fix pseudo DMA implementation, take 2 On Sun, 2 Jun 2019, Geert Uytterhoeven wrote: > Hi Finn, > > On Sun, Jun 2, 2019 at 3:29 AM Finn Thain <fthain@...egraphics.com.au> > 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@...il.com> > > Cc: Geert Uytterhoeven <geert@...ux-m68k.org> > > Cc: stable@...r.kernel.org # v4.14+ > > Fixes: 3a0f64bfa907 ("mac_scsi: Fix pseudo DMA implementation") > > Reported-by: Chris Jones <chris@...tin-jones.com> > > Tested-by: Stan Johnson <userm57@...oo.com> > > Signed-off-by: Finn Thain <fthain@...egraphics.com.au> > > 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. > 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 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.? Thanks. -- > Thanks! > > Gr{oetje,eeting}s, > > Geert > >
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