Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756630Ab0BYLAx (ORCPT ); Thu, 25 Feb 2010 06:00:53 -0500 Received: from cantor.suse.de ([195.135.220.2]:55245 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754473Ab0BYLAu (ORCPT ); Thu, 25 Feb 2010 06:00:50 -0500 Date: Thu, 25 Feb 2010 12:00:47 +0100 (CET) From: Jiri Kosina To: "Rick L. Vinyard, Jr." Cc: Oliver Neukum , =?ISO-8859-15?Q?Bruno_Pr=C3=A9mont?= , linux-input@vger.kernel.org, linux-usb@vger.kernel.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, Nicu Pavel Subject: Re: [PATCH 1/3] picolcd: driver for PicoLCD HID device In-Reply-To: Message-ID: References: <20100221002001.0a7e05a7@neptune.home> <20100224170049.0d04af3c@neptune.home> <201002241927.53532.oliver@neukum.org> User-Agent: Alpine 2.00 (LNX 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2959 Lines: 75 On Wed, 24 Feb 2010, Rick L. Vinyard, Jr. wrote: > >> +static int picolcd_raw_event(struct hid_device *hdev, > >> + struct hid_report *report, u8 *raw_data, int size) > >> +{ > >> + struct picolcd_data *data = hid_get_drvdata(hdev); > >> + char hexdata[25]; > >> + int i; > >> + > >> + if (data == NULL) > >> + return 1; > >> + > >> + for (i = 0; i < sizeof(hexdata) / 2; i++) > >> + sprintf(hexdata+2*i, "%02hhx", raw_data[i]); > >> + if (size >= sizeof(hexdata)/2) { > >> + hexdata[sizeof(hexdata)-4] = '.'; > >> + hexdata[sizeof(hexdata)-3] = '.'; > >> + hexdata[sizeof(hexdata)-2] = '.'; > >> + hexdata[sizeof(hexdata)-1] = '\0'; > >> + } else > >> + hexdata[size*2] = '\0'; > >> + > >> + switch (report->id) { > >> + case REPORT_KEYPAD: > >> + if (size == 3 && raw_data[0] == 0x11 && > >> data->input_keys) { > >> + return picolcd_raw_keypad(hdev, report, > >> raw_data+1, size-1); > >> + } else { > >> + dbg_hid(PICOLCD_NAME " unsupported key event (%d > >> bytes): 0x%s\n", size, hexdata); > >> + break; > >> + } > >> + break; > >> + case REPORT_VERSION: > >> + if (size == 3) > >> + dev_info(&hdev->dev, "Firmware version is > >> %hd.%hd\n", raw_data[1], raw_data[2]); > >> + > >> + spin_lock(&data->lock); > > > > If I recall correctly raw_event is called in interrupt. Yes, that is correct. > The issue, as I understand it is that non-interrupt code may obtain the > lock and then the interrupt code is executed... hence the deadlock and > the need to use spin_lock_irqsave() and spin_unlock_irqrestore(). Exactly. All the spinlocks that are aquired in interrupt code-paths must be acquired with _irqsave()/_irqrestore() from the non-interrupt code to prevent exactly this kind of deadlock. > > The key difference is the replacement of spin_lock() with spin_trylock() > such that if the non-interrupt code has already obtained the lock, the > interrupt will not deadlock but instead take the else path and schedule a > framebuffer update at the next interval. Why is _irqsave() and/or deferred work not enough? The aproach with _trylock() seems to be overly complicated for no good reason (I personally become very suspicious every time I see code that is using _trylock()). [ by the way, Rick, are you planning to resubmit the G13 driver with incorporated feedback from the last review round? ] Thanks, -- Jiri Kosina SUSE Labs, Novell Inc. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/