From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Shevchenko Subject: Re: 8250_dw DMA issue with BYT ? Date: Tue, 15 Apr 2014 10:25:59 +0300 Message-ID: <1397546759.11914.151.camel@smile.fi.intel.com> References: <50C3158CF44D924791C15F1437EF2EC65D9BE7@HASMSX104.ger.corp.intel.com> <20140415065606.GA3368@xps8300> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from mga11.intel.com ([192.55.52.93]:23111 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752371AbaDOH0D (ORCPT ); Tue, 15 Apr 2014 03:26:03 -0400 In-Reply-To: <20140415065606.GA3368@xps8300> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Heikki Krogerus Cc: "Poulain, Loic" , "linux-serial@vger.kernel.org" , "Jin, Yao" On Tue, 2014-04-15 at 09:56 +0300, Heikki Krogerus wrote: > On Mon, Apr 14, 2014 at 03:54:31PM +0000, Poulain, Loic wrote: ... > > This problem seems due to the DMA usage. Indeed, when I disable > > the DMA manually in 8250_dw.c (up->dma = NULL), problem does not > > occur anymore, all baudrates are stable. > > I think this is the same issue Jin Yao (CC'd) already spotted. He made > a bug for it: > https://bugzilla.kernel.org/show_bug.cgi?id=73071 > > > Do you think a specific 8250 DMA configuration could apply for the byt > > case ? > > How/Where can I debug to know if the 8250 DMA works as expected ? > > Adding Andy. He maintains the Designware DMA Engine driver that is > used on BYT. He should be the best person to tell how to debug the > DMA. In case you have DYNAMIC_DEBUG enabled in the kernel configuration you may apply following addon to the kernel command line (considering that you have DW_DMAC_CORE=y and DW_DMAC=y): dw_dmac_core.dyndbg dw_dmac.dyndbg It enables the debug messages from the dw_dmac driver. P.S. in case you need deep debugging I have a custom patch which enables it for all IO communication done with the hardware (this apparently doesn't include dumps of data transfered). -- Andy Shevchenko Intel Finland Oy