From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 196C3C4332F for ; Thu, 15 Dec 2022 01:10:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229742AbiLOBKg (ORCPT ); Wed, 14 Dec 2022 20:10:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33168 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229451AbiLOBKd (ORCPT ); Wed, 14 Dec 2022 20:10:33 -0500 Received: from mail-pj1-x1029.google.com (mail-pj1-x1029.google.com [IPv6:2607:f8b0:4864:20::1029]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7981E53ECD for ; Wed, 14 Dec 2022 17:10:32 -0800 (PST) Received: by mail-pj1-x1029.google.com with SMTP id u5so8804787pjy.5 for ; Wed, 14 Dec 2022 17:10:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=/Edze/qa0HPXemZjwOHvXFl0b/Mnz/IUyV30XlIwDVo=; b=lFO+uYcyTJOGOFVWWo1AmpohM/b0XXwNxnIoV25OB6s/a8yHFgvTRKPDtsiZXn77l4 EUiiKDhu+Nz70hAj9TqK2GzGtEhIzLCF8QdUqZ0Y8raDlUSbEEiLaXy63pHxOzaoXtTO SbfTs/IVESASf61A/v+uTCwc7s2hy2ev41GGM= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=/Edze/qa0HPXemZjwOHvXFl0b/Mnz/IUyV30XlIwDVo=; b=7Pd1BUcbdJCSzF0dZh3tX2AenK29oWIMwpE0d+/sM9ZzrdQLkpH4QvP31skRinb3N7 KDu1BvZr46QBi/cNL9igbgZEzm8Xr19FNp2P3Sfq9sNxPryPLUfvE6QNTneU+qcH6Taq FEmekNM2q1xktT0m//xZJ809oZytvIPha1qOFzguxWhUYSO9gwYNAEHGqebZ7959NGa8 /ClLhGRXA7Y2XDmTLfUPyy0g9FK8MYmZfD6R2IbIamdKVNWUGjCgUxVAGmygePkEytGG RJXHu0ZXHqy2AtEj/6bzr2r8yqbRQaH4YmXtX0UmbSausyRyBxw2mggnMJjFQl1eETVt fszQ== X-Gm-Message-State: ANoB5pk8xDN+ohskvgdM+dEDM6t17+W1A/KbVCTZb5TN8korReLvs9B+ wdpDWa+5PnrPrqfK087bo4GaIh56MqRNl4sa X-Google-Smtp-Source: AA0mqf5+6gKAHAMUtzClUJvvgj+BHiKJYtgUrqGdmygUsqSr9SFaOC3MiyoheA3VlqwrOxqZt7t6dg== X-Received: by 2002:a17:903:22c3:b0:189:d92b:86e4 with SMTP id y3-20020a17090322c300b00189d92b86e4mr38669978plg.52.1671066632042; Wed, 14 Dec 2022 17:10:32 -0800 (PST) Received: from google.com (KD124209188001.ppp-bb.dion.ne.jp. [124.209.188.1]) by smtp.gmail.com with ESMTPSA id q3-20020a170902e30300b00178143a728esm2416735plc.275.2022.12.14.17.10.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Dec 2022 17:10:30 -0800 (PST) Date: Thu, 15 Dec 2022 10:10:25 +0900 From: Sergey Senozhatsky To: Laurent Pinchart Cc: Ricardo Ribalda , Yunke Cao , Max Staudt , Mauro Carvalho Chehab , Sergey Senozhatsky , linux-kernel@vger.kernel.org, linux-media@vger.kernel.org Subject: Re: [PATCH] media: uvcvideo: Do not alloc dev->status Message-ID: References: <20221214-uvc-status-alloc-v1-0-a0098ddc7c93@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (22/12/14 14:45), Laurent Pinchart wrote: > On Wed, Dec 14, 2022 at 12:23:41PM +0100, Ricardo Ribalda wrote: > > UVC_MAX_STATUS_SIZE is 16, simplify the code by inlining dev->status. > > The reason why uvc_status is allocated dynamically is to ensure cache > line alignment, as the USB host controller may DMA to the buffer. Oh, that's a very subtle detail. > > +struct uvc_status_streaming { > > + u8 button; > > +} __packed; > > + > > +struct uvc_status_control { > > + u8 bSelector; > > + u8 bAttribute; > > + u8 bValue[11]; > > +} __packed; > > + > > +struct uvc_status { > > + u8 bStatusType; > > + u8 bOriginator; > > + u8 bEvent; > > + union { > > + struct uvc_status_control control; > > + struct uvc_status_streaming streaming; > > + }; > > +} __packed; > > + > > struct uvc_device { > > struct usb_device *udev; > > struct usb_interface *intf; > > @@ -559,7 +579,7 @@ struct uvc_device { > > /* Status Interrupt Endpoint */ > > struct usb_host_endpoint *int_ep; > > struct urb *int_urb; > > - u8 *status; > > + struct uvc_status status; So we can do something like this maybe? + struct uvc_status status ____cacheline_aligned; And this actually even improves code readability, IMHO, in a sense that we explicitly say that it has to be cache aligned.