Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753279AbbKXMDZ (ORCPT ); Tue, 24 Nov 2015 07:03:25 -0500 Received: from smtp-1b.atlantis.sk ([80.94.52.26]:35044 "EHLO smtp-1b.atlantis.sk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751864AbbKXMDX (ORCPT ); Tue, 24 Nov 2015 07:03:23 -0500 From: Ondrej Zary To: Finn Thain Subject: Re: [PATCH 00/71] More fixes, cleanup and modernization for NCR5380 drivers Date: Tue, 24 Nov 2015 13:03:17 +0100 User-Agent: KMail/1.9.10 (enterprise35 0.20100827.1168748) Cc: Sam Creasey , Michael Schmitz , "James E.J. Bottomley" , linux-m68k@vger.kernel.org, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org References: <20151118083455.331768508@telegraphics.com.au> <201511240904.55085.linux@rainbow-software.org> In-Reply-To: X-KMail-QuotePrefix: > MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <201511241303.17899.linux@rainbow-software.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3425 Lines: 81 On Tuesday 24 November 2015, Finn Thain wrote: > > On Tue, 24 Nov 2015, Ondrej Zary wrote: > > > On Tuesday 24 November 2015, Finn Thain wrote: > > > > > > 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? > > > > No 126-byte PDMA. The 126 bytes were probably lost (or mixed with the > > next read?). > > When you said, the "PDMA operation hangs waiting forever", I figured that > you had hit an infinite loop in NCR5380_pread()... but now I'm lost. The first 128-byte PDMA ended successfully (ignoring what happened to the remaining 126 bytes), then a next request for 254 bytes came. This resulted in a new 128-byte PDMA and that hanged (in one of its possibly infinite loops without a timeout). > My main concern here is to confirm that I didn't break anything e.g. with > patch 24 or 41. It would be nice to know that this hang is not the result > of a new bug. PDMA was already broken before so it's hard to tell. I can try to modify the unpatched driver to see if PDMA is broken the same way. > > The next read was also 254 bytes so another 128-byte PDMA transfer. > > > > Then modified NCR5380_information_transfer() to transfer the remaining > > data (126 bytes in this case) using PIO. It did not help, the next PDMA > > transfer failed too. > > > > AFAICT, no change to NCR5380_information_transfer() should be needed. It > was always meant to cope with the need to split a transfer between (P)DMA > and PIO. > > If the target is expecting the remaining 126 bytes, it will keep the bus > in DATA OUT phase, and the next iteration of the loop > while ((cmd = hostdata->connected)) { } > will call NCR5380_transfer_pio() for the remaining bytes. If the target > never asserts REQ, that transfer will never happen, but then the command > should timeout and get aborted, to handle the possibility that a "PDMA > operation hangs waiting forever". Thanks for explanation. > A protocol analyzer would be useful to debug this. I get a lot of value > from a bus terminator block that has LEDs for the various control signals. > Failing that, you might need to place, > #define NDEBUG (NDEBUG_INFORMATION | NDEBUG_HANDSHAKE | NDEBUG_PIO | NDEBUG_DMA | NDEBUG_MAIN) > at the top of g_NCR5380.c. -- Ondrej Zary -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/