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Date:   Thu, 15 Dec 2022 10:14:53 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     Ricardo Ribalda <ribalda@chromium.org>
Cc:     Yunke Cao <yunkec@chromium.org>, Ming Lei <tom.leiming@gmail.com>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Max Staudt <mstaudt@google.com>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        linux-kernel@vger.kernel.org, linux-media@vger.kernel.org
Subject: Re: [PATCH v2] media: uvcvideo: Do not alloc dev->status
Message-ID: <Y5p1DVWXuYSzkRO4@google.com>
References: <20221214-uvc-status-alloc-v2-0-3f1cba6fc734@chromium.org>
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In-Reply-To: <20221214-uvc-status-alloc-v2-0-3f1cba6fc734@chromium.org>
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On (22/12/14 14:37), Ricardo Ribalda wrote:
[..]
> +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 input_dev *input;
>  	char input_phys[64];
>  
> @@ -572,6 +592,12 @@ struct uvc_device {
>  	} async_ctrl;
>  
>  	struct uvc_entity *gpio_unit;
> +
> +	/*
> +	 * Ensure that status is aligned, making it safe to use with
> +	 * non-coherent DMA.
> +	 */
> +	struct uvc_status status __aligned(ARCH_KMALLOC_MINALIGN);

	____cacheline_aligned ?

I don't see anyone using ARCH_KMALLOC_MINALIGN except for slab.h