Hi Finn,
On Sun, Jun 2, 2019 at 3:29 AM Finn Thain fthain@telegraphics.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@gmail.com Cc: Geert Uytterhoeven geert@linux-m68k.org Cc: stable@vger.kernel.org # v4.14+ Fixes: 3a0f64bfa907 ("mac_scsi: Fix pseudo DMA implementation") Reported-by: Chris Jones chris@martin-jones.com Tested-by: Stan Johnson userm57@yahoo.com Signed-off-by: Finn Thain fthain@telegraphics.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?
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.
Thanks!
Gr{oetje,eeting}s,
Geert