From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: base64 Subject: dmaengine: at_xdmac: fix rare residue corruption From: Ludovic Desroches Message-Id: <20180319075916.GA2939@rfolt0960.corp.atmel.com> Date: Mon, 19 Mar 2018 08:59:16 +0100 To: Vinod Koul Cc: Ludovic Desroches , Maxime Jayat , Nicolas Ferre , Dan Williams , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org List-ID: T24gTW9uLCBNYXIgMTksIDIwMTggYXQgMDE6MjY6MDlQTSArMDUzMCwgVmlub2QgS291bCB3cm90 ZToKPiBPbiBUaHUsIE1hciAwMSwgMjAxOCBhdCAwOToyNToxNkFNICswMTAwLCBMdWRvdmljIERl c3JvY2hlcyB3cm90ZToKPiA+IEhpIE1heGltZSwKPiA+IAo+ID4gT24gVGh1LCBGZWIgMjIsIDIw MTggYXQgMTI6Mzk6NTVQTSArMDEwMCwgTWF4aW1lIEpheWF0IHdyb3RlOgo+ID4gPiBEZXNwaXRl IHRoZSBlZmZvcnRzIG1hZGUgdG8gY29ycmVjdGx5IHJlYWQgdGhlIE5EQSBhbmQgQ1VCQyByZWdp c3RlcnMsCj4gPiA+IHRoZSBvcmRlciBpbiB3aGljaCB0aGUgcmVnaXN0ZXJzIGFyZSByZWFkIGNv 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(majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755285AbeCSH7r (ORCPT ); Mon, 19 Mar 2018 03:59:47 -0400 Received: from esa2.microchip.iphmx.com ([68.232.149.84]:17820 "EHLO esa2.microchip.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754524AbeCSH7q (ORCPT ); Mon, 19 Mar 2018 03:59:46 -0400 X-IronPort-AV: E=Sophos;i="5.48,329,1517900400"; d="scan'208";a="12421413" Date: Mon, 19 Mar 2018 08:59:16 +0100 From: Ludovic Desroches To: Vinod Koul CC: Ludovic Desroches , Maxime Jayat , Nicolas Ferre , Dan Williams , , , Subject: Re: [PATCH] dmaengine: at_xdmac: fix rare residue corruption Message-ID: <20180319075916.GA2939@rfolt0960.corp.atmel.com> References: <20180222113955.4043-1-maxime.jayat@mobile-devices.fr> <20180301082516.GL22457@rfolt0960.corp.atmel.com> <20180319075608.GM15443@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20180319075608.GM15443@localhost> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Mon, Mar 19, 2018 at 01:26:09PM +0530, Vinod Koul wrote: > On Thu, Mar 01, 2018 at 09:25:16AM +0100, Ludovic Desroches wrote: > > Hi Maxime, > > > > On Thu, Feb 22, 2018 at 12:39:55PM +0100, Maxime Jayat wrote: > > > Despite the efforts made to correctly read the NDA and CUBC registers, > > > the order in which the registers are read could sometimes lead to an > > > inconsistent state. > > > > > > Re-using the timeline from the comments, this following timing of > > > registers reads could lead to reading NDA with value "@desc2" and > > > CUBC with value "MAX desc1": > > > > > > INITD -------- ------------ > > > |____________________| > > > _______________________ _______________ > > > NDA @desc2 \/ @desc3 > > > _______________________/\_______________ > > > __________ ___________ _______________ > > > CUBC 0 \/ MAX desc1 \/ MAX desc2 > > > __________/\___________/\_______________ > > > | | | | > > > Events:(1)(2) (3)(4) > > > > > > (1) check_nda = @desc2 > > > (2) initd = 1 > > > (3) cur_ubc = MAX desc1 > > > (4) cur_nda = @desc2 > > > > > > This is allowed by the condition ((check_nda == cur_nda) && initd), > > > despite cur_ubc and cur_nda being in the precise state we don't want. > > > > > > This error leads to incorrect residue computation. > > > > > > Fix it by inversing the order in which CUBC and INITD are read. This > > > makes sure that NDA and CUBC are always read together either _before_ > > > INITD goes to 0 or _after_ it is back at 1. > > > The case where NDA is read before INITD is at 0 and CUBC is read after > > > INITD is back at 1 will be rejected by check_nda and cur_nda being > > > different. > > > > > > Fixes: 53398f488821 ("dmaengine: at_xdmac: fix residue corruption") > > > Cc: stable@vger.kernel.org > > > Signed-off-by: Maxime Jayat > > > > Nice work! I agree with the change you propose. > > > > I am disappointed we didn't spot this case so I would like to double-check with > > the hardware guy there is no issue with the sequence you propose. That's > > why I am waiting a bit before giving my ack. > > any update on that? This has been pending for a while... Unfortunately not. As I am pretty confident in Maxime patch: Acked-by: Ludovic Desroches > > > > > Regards > > > > Ludovic > > > > > --- > > > Hi, > > > > > > I had a bug where the serial ports on the Atmel SAMA5D2 were sometimes > > > returning the same data twice, for up to 4096 bytes. > > > > > > After investigation, I noticed that the ring buffer used in > > > atmel_serial (in rx dma mode) had sometimes a incorrect "head" value, > > > which made the ring buffer do a complete extraneous loop of data > > > pushed to the tty layer. > > > > > > I tracked it down to the residue of the dma being wrong, and after > > > more head scratching, I found this bug in the reading of the > > > registers. > > > > > > Before fixing this, I was able to reproduce the bug reliably in a few > > > minutes. With this patch applied, the bug did not reappear after > > > several hours in testing. > > > > > > > > > drivers/dma/at_xdmac.c | 4 ++-- > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c > > > index c00e3923d7d8..94236ec9d410 100644 > > > --- a/drivers/dma/at_xdmac.c > > > +++ b/drivers/dma/at_xdmac.c > > > @@ -1471,10 +1471,10 @@ at_xdmac_tx_status(struct dma_chan *chan, dma_cookie_t cookie, > > > for (retry = 0; retry < AT_XDMAC_RESIDUE_MAX_RETRIES; retry++) { > > > check_nda = at_xdmac_chan_read(atchan, AT_XDMAC_CNDA) & 0xfffffffc; > > > rmb(); > > > - initd = !!(at_xdmac_chan_read(atchan, AT_XDMAC_CC) & AT_XDMAC_CC_INITD); > > > - rmb(); > > > cur_ubc = at_xdmac_chan_read(atchan, AT_XDMAC_CUBC); > > > rmb(); > > > + initd = !!(at_xdmac_chan_read(atchan, AT_XDMAC_CC) & AT_XDMAC_CC_INITD); > > > + rmb(); > > > cur_nda = at_xdmac_chan_read(atchan, AT_XDMAC_CNDA) & 0xfffffffc; > > > rmb(); > > > > > > -- > > > 2.14.1 > > > > > -- > ~Vinod