From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tony Lindgren Subject: Re: [PATCH v7] 8250-core based serial driver for OMAP + DMA Date: Fri, 15 Aug 2014 13:28:27 -0700 Message-ID: <20140815202826.GC9239@atomide.com> References: <1408124563-31541-1-git-send-email-bigeasy@linutronix.de> <20140815181704.GH17769@csclub.uwaterloo.ca> <53EE5BF8.3010007@linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mho-03-ewr.mailhop.org ([204.13.248.66]:64266 "EHLO mho-01-ewr.mailhop.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751063AbaHOU2g (ORCPT ); Fri, 15 Aug 2014 16:28:36 -0400 Content-Disposition: inline In-Reply-To: <53EE5BF8.3010007@linutronix.de> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Sebastian Andrzej Siewior Cc: Lennart Sorensen , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org, balbi@ti.com, Vinod Koul , Greg Kroah-Hartman * Sebastian Andrzej Siewior [140815 12:16]: > On 08/15/2014 08:17 PM, Lennart Sorensen wrote: > > > Are you saying that with the new driver you have to respond to the RX > > irq faster than before to avoid overflows? It is not quite clear. > > Yes. The irq fires 46 bytes giving you 16 bytes buffer before overflow > vs 63 bytes buffer the old one had. > > > I do think 40000 interrupts to handle 40000 bytes of date does seem a > > tad inefficient, so dropping to 854 looks a lot nicer. Was the omap > > driver not using the fifo trigger levels at all? > > It configured the trigger levels to 1 for RX and 16 for TX. Hmm that weird RX trigger level is a workaround for lost characters. See commit 0ba5f66836 (tty: serial: OMAP: use a 1-byte RX FIFO threshold in PIO mode :) There's paste test in that commit, I wonder if the 8250 drivers can deal with it any better? Regards, Tony