Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758226Ab0BXVpM (ORCPT ); Wed, 24 Feb 2010 16:45:12 -0500 Received: from mail.cs.nmsu.edu ([128.123.64.3]:34934 "EHLO mail.cs.nmsu.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758176Ab0BXVpJ (ORCPT ); Wed, 24 Feb 2010 16:45:09 -0500 Message-ID: In-Reply-To: <201002241927.53532.oliver@neukum.org> References: <20100221002001.0a7e05a7@neptune.home> <20100224170049.0d04af3c@neptune.home> <201002241927.53532.oliver@neukum.org> Date: Wed, 24 Feb 2010 14:44:53 -0700 Subject: Re: [PATCH 1/3] picolcd: driver for PicoLCD HID device From: "Rick L. Vinyard, Jr." To: "Oliver Neukum" Cc: Bruno =?iso-8859-1?Q?Pr=C3=A9mont?= , "Jiri Kosina" , linux-input@vger.kernel.org, linux-usb@vger.kernel.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, "Nicu Pavel" User-Agent: SquirrelMail/1.4.19 MIME-Version: 1.0 Content-Type: text/plain;charset=iso-8859-1 Content-Transfer-Encoding: 8bit X-Priority: 3 (Normal) Importance: Normal Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4240 Lines: 134 Oliver Neukum wrote: > Am Mittwoch, 24. Februar 2010 17:00:49 schrieb Bruno Prémont: >> +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. As you take a > spinlock here, > the lock in code not called in interrupt must disable interrupts, or you > may > deadlock. > 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(). If that is correct, is there any problem with the following approach? 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. static void g13_fb_urb_completion(struct urb *urb) { struct g13_data *data = urb->context; spin_unlock(&data->fb_urb_lock); } static int g13_fb_send(struct hid_device *hdev) { struct usb_interface *intf; struct usb_device *usb_dev; struct g13_data *data = hid_get_g13data(hdev); struct usb_host_endpoint *ep; unsigned int pipe; int retval = 0; /* * Try and lock the framebuffer urb to prevent access if we have * submitted it. If we can't lock it we'll have to delay this update * until the next framebuffer interval. * * Fortunately, we already have the infrastructure in place with the * framebuffer deferred I/O driver to schedule the delayed update. */ if (likely(spin_trylock(&data->fb_urb_lock))) { /* Get the usb device to send the image on */ intf = to_usb_interface(hdev->dev.parent); usb_dev = interface_to_usbdev(intf); pipe = usb_sndintpipe(usb_dev, 0x02); ep = usb_dev->ep_out[usb_pipeendpoint(pipe)]; if (unlikely(!ep)) { spin_unlock(&data->fb_urb_lock); return -EINVAL; } pipe = (pipe & ~(3 << 30)) | (PIPE_INTERRUPT << 30); usb_fill_int_urb(data->fb_urb, usb_dev, pipe, data->fb_vbitmap, G13_VBITMAP_SIZE, g13_fb_urb_completion, NULL, ep->desc.bInterval); data->fb_urb->context = data; data->fb_urb->actual_length = 0; retval = usb_submit_urb(data->fb_urb, GFP_NOIO); if (unlikely(retval < 0)) { /* * We need to unlock the framebuffer urb lock since * the urb submission failed and therefore * g13_fb_urb_completion() won't be called. */ spin_unlock(&data->fb_urb_lock); return retval; } } else { schedule_delayed_work(&data->fb_info->deferred_work, data->fb_defio.delay); } return retval; } Thanks, -- Rick -- 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/