linux-kernel - Re: [PATCH 00/71] More fixes, cleanup and modernization for NCR5380 drivers

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Message-ID: <alpine.LNX.2.00.1511241219430.28883@nippy.intranet>
Date:	Tue, 24 Nov 2015 12:21:18 +1100 (AEDT)
From:	Finn Thain <fthain@...egraphics.com.au>
To:	Ondrej Zary <linux@...nbow-software.org>
cc:	Sam Creasey <sammy@...my.net>,
	Michael Schmitz <schmitzmic@...il.com>,
	"James E.J. Bottomley" <JBottomley@...n.com>,
	linux-m68k@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/71] More fixes, cleanup and modernization for NCR5380
 drivers


On Mon, 23 Nov 2015, Ondrej Zary wrote:

> 
> PDMA seems to be broken in multiple ways. NCR5380_pread cannot process 
> less than 128 bytes. In fact, 53C400 datasheet says that it's HW 
> limitation: non-modulo-128-byte transfers should use PIO.
> 
> Adding
>         transfersize = round_down(transfersize, 128);
> to generic_NCR5380_dma_xfer_len() improves the situation a bit.
> 
> After modprobe, some small reads (8, 4, 24 and 64 bytes) are done using 
> PIO, then eight 512-byte reads using PDMA and then it fails on a 
> 254-byte read. First 128 bytes are read using PDMA and the next PDMA 
> operation hangs waiting forever for the host buffer to be ready.
> 

A 128-byte PDMA receive followed by 126-byte PDMA receive? I don't see how
that is possible given round_down(126, 128) == 0. Was this the actual
'len' argument to NCR5380_pread() in g_NCR5380.c?

BTW, I presume that FLAG_NO_DMA_FIXUPS was set (which is the case if you
pass ncr_53c400=1 option with modprobe). Otherwise you could see PDMA IO
sizes like 127 etc.

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