Re: [PATCH v3 0/4] g_NCR5380: PDMA fixes and cleanup

From: Finn Thain
Date: Wed Jun 28 2017 - 00:10:42 EST


On Tue, 27 Jun 2017, Ondrej Zary wrote:

> On Tuesday 27 June 2017 14:42:29 Finn Thain wrote:
>
> > > ... it triggers sometimes: the value is 1 instead of 0. As we use
> > > only 16-bit writes, I don't see how the value could ever be odd.
> > > Looks like a bug in the chip. The index register corrupts during the
> > > transfer, not after IRQ or timeout. The same check at beginning of
> > > pwrite() did not trigger.
> >
> > Are you reading this register at the right moment? Have you tried
> > waiting for it to reach zero, as in,
> >
> > if (NCR5380_poll_politely(hostdata, 13, 0xff, 0, HZ / 64) < 0)
> > /* printk, reset etc */;
>
> I have not but will try (expecting that it will not change by itself).
>

Now that I know that it is the byte at the beginning of the block that
went missing, I agree that there's no point waiting for the byte count to
change.

I've included a patch with your 512 B limit in v4.

Thanks.

> > Even if this is a reliable way to detect a short transfer, it would be
> > nice to know the root cause. But I'm being unrealistic: the DTC436
> > vendor never responded to my requests for technical documentation.
>
> According to the data corruption observed, it's not a short transfer.
> The corruption is always the same: one byte missing at the beginning of
> a 128 B block. It happens only with slow Quantum LPS 240 drive, not with
> faster IBM DORS-32160.
>

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