Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <46e0aac3-e238-1f32-264c-eed8a849d156@wolfvision.net>
Date:   Tue, 6 Jun 2023 15:15:33 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.11.0
Subject: Re: [PATCH RFC v2 2/6] media: v4l2-ctrls: clarify documentation of
 V4L2_CID_FOCUS_RELATIVE
Content-Language: en-US
To:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        libcamera-devel@lists.libcamera.org,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Matthias Fend <Matthias.Fend@wolfvision.net>,
        Dave Stevenson <dave.stevenson@raspberrypi.com>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20230406-feature-controls-lens-v2-0-faa8ad2bc404@wolfvision.net>
 <20230406-feature-controls-lens-v2-2-faa8ad2bc404@wolfvision.net>
 <20230606103618.GB25774@pendragon.ideasonboard.com>
From:   Michael Riesch <michael.riesch@wolfvision.net>
Organization: WolfVision GmbH
In-Reply-To: <20230606103618.GB25774@pendragon.ideasonboard.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?eW5IRGlGck5KMytmQmZEbVhjc1ZCT2YzUlZhZXcwbi9oRmJTVnJHaE5HRTZ6?=
 =?utf-8?B?NHBzME1IVjBNUGRLQVNrekVPeDlSUjBJaGVrOUJXZTdtMk1HRVVHZjlTd0FW?=
 =?utf-8?B?UlJNRWpoYk04Q3gxYThXd1djeCtOT3U1R3pGSDhaUHhBd1dVUzQxbm5BMG1I?=
 =?utf-8?B?ZXk2RzN1cDYxN21waitkQ2Q0MHhIeXVZMjZKNkJjVU41V0pXbE9wVS9kZjNi?=
 =?utf-8?B?TG5KQ3AvUS9YZ2RvUDl1cE5zNG1kdlBIZ0llekFROVlYOGJDZmV3dVB3YmFz?=
 =?utf-8?B?NjhndXpVeEs0ejBDMHR0UWRRMUFENUJIL2FkRFR2aHdvWHpjRzAvTWNDdGEz?=
 =?utf-8?B?S3VaSWIwRG5FVFBCSVJBQ21XdlFqSVoxdmVJTWFHSVp0S0o5YUlZWVBBa2Uz?=
 =?utf-8?B?VmxjWkF3RFhHQWlRK2luRE1wQnYybWNwWjFHSHllL2RwR0FpM1VlYW5uMVlT?=
 =?utf-8?B?bVhjVE1FRElRUEltK29DYXVpTWJzVFNzOWtTbnl4ZFFDdmhEMHRxOHNQaEQv?=
 =?utf-8?B?OERESlBDYjN4SjlZL1lnMjRZUG41K0FwdGZ2MEdzb0JzN1Z1ZE1HYmxncHRL?=
 =?utf-8?B?a1FWVWRpYTg0bjJjWG5ST1ZpdTk5L0xhNHhlNElvTkwyRmJlYisxL1ZxYzdu?=
 =?utf-8?B?RkMxQko5ZmRwTEpWZHo2aGplMmpiVC9IOVlBMEx0bkFvYnQ3cnFWMWpzZkFr?=
 =?utf-8?B?QjYzMzlDZzB6MGJRK1Ivc2xNeWI1TVVDS0JLcTRqREkrd01VSlFUMHhSWFR4?=
 =?utf-8?B?YzgyQlJHdk1Jak9jOFhlMU9vcklNY1psR0tDOWRRSCsyN2x4WXYyUGJjZ0hE?=
 =?utf-8?B?c2xJcmJjOXZzZDNFcWx3U0pRVXRYUDJGMmF0aUw1U0JJcld4K2d0YUltVlVT?=
 =?utf-8?B?NEZEZ0IyTmd6VW1rWkUvbC81Q3hjM2kvdXFEV2p4MmVGdUJCSUxLZ3E5SUla?=
 =?utf-8?B?dXN0RHNoVW1vQ0ZqU3NqNkdIOHNIandTVTBRS2hQUFBGN0lLbjh2Yzl0RnR5?=
 =?utf-8?B?U1JsMHhQQWpPK2hOcUtPc2pXaitNd2xRZnNwOHdZdDd5TXlPUjRmWkdNcWRP?=
 =?utf-8?B?cGxseWZuRENLOUdlcXhnanZxNzBXbUV1WjdhWlRpY0ZqSDZRUVRFL2g0ZEdz?=
 =?utf-8?B?ZDVDRithc3psSkcydUlRYnpmSmsybUtKTVllSzY4bDBOclcybjdGQkZUQjht?=
 =?utf-8?B?RkRObVJJY2RZWHNta2dwK3BYNTZYa1Q3Y0I0ZXF0b3NBR0loZnBtUkJuc1RM?=
 =?utf-8?B?NnVJZHRPa1BBbVlUWWNwZ0EyY0d2dXc3NTNOdUVCbTdpWUVQVmRmR1FiUDZB?=
 =?utf-8?B?NVFSWTVJNm1iU284TVI1S1NBa0F4NS9LZkxjUFFEVm5CZXpybU9XdmNSQUpo?=
 =?utf-8?B?SlhpR0VzRTlLeWhBd3I3dXlxQ3R3WUp5Q1JvZTI1UnZaclhkUnVSSzRaRU9U?=
 =?utf-8?B?OEhEWGtDbnphQ2h5ZzVMcUcrZlZsZGlJeWtXWUJSUll4aXBsdmVqak5XNWVl?=
 =?utf-8?B?TmNZQVkySnFub3BIZ0dhaXlwRUNZanlWSWExUnp6MmZSSUdpYUV3S09DQ3JJ?=
 =?utf-8?B?L0VDMWszSVRpQ3ZjREcrYUI5NzAzVEdCZVVvZ01INk5YeGVJWXFaV2RNVnRE?=
 =?utf-8?B?UUhZQ0VZS3VKRDFLM0ZTWlBTblJNOWc4VnI5ODd0eXdIQWg5NERZMkd4UE5D?=
 =?utf-8?B?R2FKMGxhQ1lyK1ZySHg0ckJhNDF0a3BycHpUOFl0dERwYzRVZ3pHMXlTUmM5?=
 =?utf-8?B?NWdLYjFuSDlqUnRzdjVrMThmT2RxbWtLWXJ2aXQ0SXpkNG0zVFdSYVhTTEpB?=
 =?utf-8?B?bHE0R0pGTndLNTFxQTZ0Q0liVGxqa242aXA1V1g4RnNjcVVlZXFtWERyRzMx?=
 =?utf-8?B?SGFBRzRtZC9iUVBJcHNucjZJUWNKczIzbFNjMlF0dVFyOFIwZXZhZ3I5Tkhl?=
 =?utf-8?B?R3lPeElyWUR3YkR1NGRLWitMaFk5dFVGeGRiT25YU01iQ1F3MkRMdndUUkx4?=
 =?utf-8?B?YTBQQkNIdjRIbzBZaEZJMVdSWHB4SU9nV0VtZXR0dzIxSmtDdFRvYkYvL3Nl?=
 =?utf-8?B?czNRVlB1OGVTK0ZtN1N3MXFZSEVneXcyZEtzL2dOaVRkdHBHcDBHTlRDREZV?=
 =?utf-8?B?RTQrY2tPT3I1dERYWlhQTkdrYkFEY1JOZms2a1JoS2VYVXp3dE9HMGpUNjJr?=
 =?utf-8?B?N0E9PQ==?=
X-OriginatorOrg: wolfvision.net
X-MS-Exchange-CrossTenant-Network-Message-Id: 8eb6d506-5a0d-496a-49df-08db66901d97
X-MS-Exchange-CrossTenant-AuthSource: DU0PR08MB9155.eurprd08.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Jun 2023 13:15:36.2399
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: e94ec9da-9183-471e-83b3-51baa8eb804f
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: 0b4/YbK+mC5keGT5yc1MY2hsqXrl+pQ4eQUNRdr7fhFO3+6F92bBXe5bj6KlnLu4kpxXK4pY9FGo8631uIS3VyYa38Qe2KaukSx0fx1HHiM=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV2PR08MB8461
X-Spam-Status: No, score=-2.2 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,RCVD_IN_DNSWL_NONE,
        RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_PASS,T_SCC_BODY_TEXT_LINE,
        URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hi Laurent,

On 6/6/23 12:36, Laurent Pinchart wrote:
> Hi Michael,
> 
> Thank you for the patch.
> 
> On Tue, Apr 25, 2023 at 11:45:12AM +0200, Michael Riesch wrote:
>> The control V4L2_CID_FOCUS_RELATIVE only makes sense if the device cannot
>> handle absolute focal point positioning with V4L2_CID_FOCUS_ABSOLUTE.
>> Clarify this in the documentation.
>>
>> Signed-off-by: Michael Riesch <michael.riesch@wolfvision.net>
>> ---
>>  Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst
>> index df29150dce7b..42cf4c3cda0c 100644
>> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst
>> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst
>> @@ -147,7 +147,9 @@ enum v4l2_exposure_metering -
>>      This control moves the focal point of the camera by the specified
>>      amount. The unit is undefined. Positive values move the focus closer
>>      to the camera, negative values towards infinity. This is a
>> -    write-only control.
>> +    write-only control. It should be implemented only if the device cannot
>> +    handle absolute values.
>> +
> 
> Extra blank line.

Will fix that.

> I don't think this is right. The control was added for the UVC driver,
> and there are devices that implement both absolute and relative focus.

I am by no means an expert here and just following Sakari's suggestion
here (see [0]). I can drop the patch, leave it as-is, or modify it.
Whatever makes sense to you guys. But maybe I should leave this to
someone more knowledgeable in this area and drop the patch from my
series. The changes above are completely orthogonal to my work.

Best regards,
Michael

> 
>>  
>>  ``V4L2_CID_FOCUS_AUTO (boolean)``
>>      Enables continuous automatic focus adjustments. The effect of manual
>>
> 

[0] https://lore.kernel.org/all/ZDbChgZJHVaaX3%2Fx@kekkonen.localdomain/