From mboxrd@z Thu Jan 1 00:00:00 1970 From: Krzysztof Kozlowski Subject: Re: [PATCH 0/3] serial: samsung: Fix UART status handling and other fixes Date: Thu, 10 Sep 2015 09:23:39 +0900 Message-ID: <55F0CD8B.8080403@samsung.com> References: <1441705127-24125-1-git-send-email-r.baldyga@samsung.com> <55EF7395.2000702@samsung.com> <55EFF898.7060205@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-reply-to: <55EFF898.7060205@samsung.com> Sender: linux-kernel-owner@vger.kernel.org To: Robert Baldyga , gregkh@linuxfoundation.org Cc: jslaby@suse.com, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, m.szyprowski@samsung.com List-Id: linux-serial@vger.kernel.org On 09.09.2015 18:15, Robert Baldyga wrote: > On 09/09/2015 01:47 AM, Krzysztof Kozlowski wrote: >> On 08.09.2015 18:38, Robert Baldyga wrote: >>> Hello, >>> >>> This patch set contains three patches: two minor fixes and one quite >>> important bugfix enabling UART status handling in DMA mode, which was >>> missing so far. It enables, among others, 'break' contition handling, >>> which is necessary if we want to use Magic SysRq. So this patch fixes >>> Magic SysRq handling for serial consoles using UART in DMA mode, >> >> Is it even worth using UART for serial console in DMA mode? How many >> benefits it brings? Anyone measured real data? >> >> The patch which enabled DMA for all serial ports on Exynos4 uncovered >> some issues. That is one benefit... but was it worth it? > > Well, UART in DMA mode should work at least as good as in PIO, so there > is nothing wrong in having serial console configured in DMA. Sure, it > rather barely reduces number of interrupts while used as typical serial > console, but in some cases (eg. using zmodem) it can be more profitable. That's some reason... and mentioned earlier testing of DMA which uncovered some interesting issues. :) > > To be honest, I have no strong feeling about that. I've decided to > utilize new possibility opened by introducing DMA mode in serial driver, > so I've send patch enabling it for each port on Exynos4. But if it > turned out to be unneeded I will not insist on it. I was just thinking loud... I don't have any data neither so let's go ahead with serial DMA. Best regards, Krzysztof