From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Cox Subject: Re: [PATCH] serial: 8250 check iir rdi in interrupt Date: Fri, 26 Oct 2012 15:19:02 +0100 Message-ID: <20121026151902.0a382d16@pyramind.ukuu.org.uk> References: <20121023110133.62bed522@pyramind.ukuu.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from lxorguk.ukuu.org.uk ([81.2.110.251]:55383 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933043Ab2JZOOA (ORCPT ); Fri, 26 Oct 2012 10:14:00 -0400 In-Reply-To: Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Min Zhang Cc: gregkh@linuxfoundation.org, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org > It is racing. For "too much work for irq", here is sequence events > analyzed by a Motorola engineer: Thanks - this is enormously helpful in understanding the report. > 5) The LSR indicates that the transmitter needs data, > but also indicates the presence of data in the FIFO (0x61 in the LSR) > 6) The processing function receives the characters, and > outputs data to the FIFO > 7) At the exact time (very very small window) that the > character is read from the FIFO, the FIFO timeout occurs locking in an > interrupt cause > 8) The next loop through the interrupt code begins > 9) The IIR now indicates the data timeout interrupt > (0xCC in the IIR) > 10) The processing function is called and it reads the > LSR > 11) The LSR is 0 indicating nothing to do > 12) The interrupt loop continues (the IIR won't clear > until a character is pulled) until it reaches its max count and > displays the error. So we only need to check this in serial8250_handle_irq when IIR indicates a data timeout interrupt ? Can we do if ((iir & 0x0F) == 0x0C) { /* Expensive RDI check */ } Alan