Received-SPF: pass (google.com: domain of linux-kernel+bounces-95400-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:40f1:3f00::1 as permitted sender) client-ip=2604:1380:40f1:3f00::1;
Message-ID:
 <SEZPR06MB6959882F5DA673456A3AA85D96202@SEZPR06MB6959.apcprd06.prod.outlook.com>
Date: Thu, 7 Mar 2024 19:18:05 +0800
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v3] clk: set initial best mux parent to current parent
 with CLK_MUX_ROUND_CLOSEST
Content-Language: en-US
To: Maxime Ripard <mripard@kernel.org>
Cc: Michael Turquette <mturquette@baylibre.com>,
 Stephen Boyd <sboyd@kernel.org>, linux-clk@vger.kernel.org,
 linux-kernel@vger.kernel.org
References: <20240307-mux-v3-1-0885fc1ab2c9@outlook.com>
 <20240307-hot-hummingbird-of-atheism-87503c@houat>
From: Yang Xiwen <forbidden405@outlook.com>
In-Reply-To: <20240307-hot-hummingbird-of-atheism-87503c@houat>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk
MIME-Version: 1.0
X-MS-Exchange-MessageSentRepresentingType: 1
X-MS-PublicTrafficType: Email
X-MS-TrafficTypeDiagnostic: SEZPR06MB6959:EE_|TY0PR06MB5610:EE_
X-MS-Office365-Filtering-Correlation-Id: 43a4c4d5-c6be-49cc-a22a-08dc3e9844cd
X-Microsoft-Antispam: BCL:0;
X-Microsoft-Antispam-Message-Info:
	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
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0:
	=?utf-8?B?SjJEK0VlaXhJckNtZTkrdEpKUGZrWU5OUnFBd1RqU2J5Q3lodG0zR2ExQjkw?=
 =?utf-8?B?cjhCQ2l0QlQ5UGNkVm5lZFpUZ2IxN240eWJSR0pqTk9QWWYyekdnY25VN1JJ?=
 =?utf-8?B?V0hvdHBYUnczWWF2SWM1L3NVYkE4Sm9JZ2o5SUQ4N3h5aE1tWVdBM2phVGhI?=
 =?utf-8?B?MmtUTWtGRFRIVUpPalZ4VEZiUjEyejRsRUhvR015dVlia3lqVnptOFgzMGsy?=
 =?utf-8?B?czFXWXhCWUdVNmpmR3pHME54dlJXUE1VZFdZelEzVW9QamZMQmJHUDNBVzVv?=
 =?utf-8?B?bEZtU0cwZ09xM0NJenRMS3g3bW0vMkVUTSsyNUI0dmlZUkp3bG1Tb3dPcVFz?=
 =?utf-8?B?bHJWRlV2OURhWU5jbGxvbGhRNjhOVEtuTGRDTE1iSFYrWldxeGxFOWh4YktG?=
 =?utf-8?B?UXJjMFd0Um5KdDVnelhOWDkxTnhsdDRvdDBFaEN3M28xdkhLcHBudm5PK2Zp?=
 =?utf-8?B?QnZBL1lCOENSSE81cTRQZFVnMXBCVFJtb0tMdVgyYnV3YVBNNlVRUmVTRjNt?=
 =?utf-8?B?VVRuWHVPWW51eThMQ2t5ZXViNUtvSTh4STVNQlBvZis0ZGFjWTNHWGgyOHBu?=
 =?utf-8?B?OEhWT0ZySzJIZDNkMVlwaU90ODhIQlg5TnpSME9tRU5uWHVHS3VVMm9hbi9X?=
 =?utf-8?B?YzcrQWpWRmhEbStwa3hzdjBrV3NacG1XZlRoZ0Q4TmRGeThDYmdkRWk1NjNL?=
 =?utf-8?B?SFZ6aUo3TlNHZ1h4RXExWndUQ25KbUJPY0d2VTByUjdBRXVXQzl4dkFrQWtm?=
 =?utf-8?B?eHdZVjBMeDVWZmpqVGNwZ3ZYVC9KbnRjV2VWdUpZWXNkb2R4T1hKbWJTdmxH?=
 =?utf-8?B?VHlRbTluQVdDeDl0TVcvK21qTTExMUVKVEM5N3diU2dXZEY5WS91K1F2TmJ0?=
 =?utf-8?B?Vi8zVjdkakxWVWdmckhEY1JZVHZQQkNJeWJYMHBZSGhQZTFmclR1UmJITG5Q?=
 =?utf-8?B?clBkbzQrVDVwZzcvVURsTzgwOTVWcC92Z084RmsraENmMGJ2Nkh4aThhczZP?=
 =?utf-8?B?YW1CMmpqRWJtWnNCKzFSUXpWS083cjhRWVVCT2U0L1BESENqMU9lTkxCUnp2?=
 =?utf-8?B?RjdyWC9wMGhaTXdwN0lJLzAzRzMxc2NWbVhxcExQalBMT1FUOWRjaGtrWXo5?=
 =?utf-8?B?dFRyMGxEcDZoSjVBY1pIVlZCSkxJSFN4WXRnOUMvMFY5TENNdEpEaEs0cWJP?=
 =?utf-8?B?UTFGdWZKMnJOYm5FaE5GbVZwMlRISG9PQlN6T0JkVmFrM3hBbUhqWXpQMk4z?=
 =?utf-8?B?dDBiZGF0QllVQ2g1aXpaNFloRWVuNTdMUm5mc3QyelZrdXJONDFYMHJsNTdh?=
 =?utf-8?B?S0ljdkY5ck1OUUJ6bmRpK3hDeWc5dG84NEg5SGVpNGlvVjM4YTVRQ2xtMkYy?=
 =?utf-8?B?UnZ4ZzhPSDJwb1BtRGJMOU1rbmpkZFBoeWp6dHJWRUE2TlVzcUF6eG1PTFhZ?=
 =?utf-8?B?OXNqbnZvc2h1Mk9pRkVKc0gxSjMzb0d1VGVUc2ovbjJTMjhkemJaU0xSaW9X?=
 =?utf-8?B?cDRkbUsreHZQdit0WE1mYnh1Q1laeW5BV0oycCsvc2VZbVE1OWNBeFlEZ0h2?=
 =?utf-8?B?dXVLcmtoUEppQm5FeGFhYmJzL09Mejl1TllNN2JYVGhIaG85UkN4cExlZHRU?=
 =?utf-8?B?NjV0blFyZWNVZEt3czVBSTlOam5QM0haKzlxMlBNTlUzcVNWWkJKL3pRVUFM?=
 =?utf-8?B?RWVERXh0b3E2dXBDOXFOTnJJZ21wd1ZQUU9KR0YyVCtzeCtKUnBoSGQ1SkRX?=
 =?utf-8?Q?H6uaLtMPRNNCwVC9jy/AqzPnDjq31dP7YPbXt3/?=
X-OriginatorOrg: outlook.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 43a4c4d5-c6be-49cc-a22a-08dc3e9844cd
X-MS-Exchange-CrossTenant-AuthSource: SEZPR06MB6959.apcprd06.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Mar 2024 11:18:09.2298
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 84df9e7f-e9f6-40af-b435-aaaaaaaaaaaa
X-MS-Exchange-CrossTenant-RMS-PersistedConsumerOrg:
	00000000-0000-0000-0000-000000000000
X-MS-Exchange-Transport-CrossTenantHeadersStamped: TY0PR06MB5610

On 3/7/2024 4:48 PM, Maxime Ripard wrote:
> Hi,
>
> On Thu, Mar 07, 2024 at 10:03:50AM +0800, Yang Xiwen via B4 Relay wrote:
>> From: Yang Xiwen <forbidden405@outlook.com>
>>
>> Originally, the initial clock rate is hardcoded to 0, this can lead to
>> some problem when setting a very small rate with CLK_MUX_ROUND_CLOSEST.
>>
>> For example, if the lowest possible rate provided by the mux is 1000Hz,
>> setting a rate below 500Hz will fail, because no clock can provide a
>> better rate than the non-existant 0Hz. But it should succeed with 1000Hz
>> being set.
>>
>> Setting the initial best parent to current parent could solve this bug.
>>
>> Signed-off-by: Yang Xiwen <forbidden405@outlook.com>
> I don't think it would be the way to go. The biggest issue to me is that
> it's inconsistent, and only changing the behaviour for a given flag
> doesn't solve that.


I think the current behavior is odd but conforms to the document if 
CLK_MUX_ROUND_CLOSEST is not specified. If i understand correctly, the 
default behavior of mux clocks is to select the closest rate lower than 
requested rate, and CLK_MUX_ROUND_CLOSEST removes the "lower than" 
limitation, which is what this version tries to accomplish.


>
> And again, either way, we should document it. And run it through kernelci.
>
> Maxime


-- 
Regards,
Yang Xiwen