Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.33 as permitted sender) client-ip=23.128.96.33;
Message-ID: <42ad3f60-2755-4d3b-a766-8e4404f76a7c@linaro.org>
Date:   Wed, 15 Nov 2023 22:00:17 +0100
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH 1/4] dt-bindings: reset: Add binding for Sophgo CV1800B
 reset controller
To:     Jisheng Zhang <jszhang@kernel.org>, Conor Dooley <conor@kernel.org>
Cc:     Samuel Holland <samuel.holland@sifive.com>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Chao Wei <chao.wei@sophgo.com>,
        Chen Wang <unicorn_wang@outlook.com>,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org
References: <20231113005503.2423-1-jszhang@kernel.org>
 <20231113005503.2423-2-jszhang@kernel.org>
 <44f21244-5bf1-4e0f-80a9-6ec76d65eea4@linaro.org> <ZVTHMsXaPdHiuUOF@xhacker>
 <80e28d77-4a0e-4827-91c0-951094176bbd@sifive.com>
 <20231115-upward-unsworn-7746e0aeb5dd@squawk> <ZVTgfzeK6GkKpArK@xhacker>
Content-Language: en-US
From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Autocrypt: addr=krzysztof.kozlowski@linaro.org; keydata=
 xsFNBFVDQq4BEAC6KeLOfFsAvFMBsrCrJ2bCalhPv5+KQF2PS2+iwZI8BpRZoV+Bd5kWvN79
 cFgcqTTuNHjAvxtUG8pQgGTHAObYs6xeYJtjUH0ZX6ndJ33FJYf5V3yXqqjcZ30FgHzJCFUu
 JMp7PSyMPzpUXfU12yfcRYVEMQrmplNZssmYhiTeVicuOOypWugZKVLGNm0IweVCaZ/DJDIH
 gNbpvVwjcKYrx85m9cBVEBUGaQP6AT7qlVCkrf50v8bofSIyVa2xmubbAwwFA1oxoOusjPIE
 J3iadrwpFvsZjF5uHAKS+7wHLoW9hVzOnLbX6ajk5Hf8Pb1m+VH/E8bPBNNYKkfTtypTDUCj
 NYcd27tjnXfG+SDs/EXNUAIRefCyvaRG7oRYF3Ec+2RgQDRnmmjCjoQNbFrJvJkFHlPeHaeS
 BosGY+XWKydnmsfY7SSnjAzLUGAFhLd/XDVpb1Een2XucPpKvt9ORF+48gy12FA5GduRLhQU
 vK4tU7ojoem/G23PcowM1CwPurC8sAVsQb9KmwTGh7rVz3ks3w/zfGBy3+WmLg++C2Wct6nM
 Pd8/6CBVjEWqD06/RjI2AnjIq5fSEH/BIfXXfC68nMp9BZoy3So4ZsbOlBmtAPvMYX6U8VwD
 TNeBxJu5Ex0Izf1NV9CzC3nNaFUYOY8KfN01X5SExAoVTr09ewARAQABzTRLcnp5c3p0b2Yg
 S296bG93c2tpIDxrcnp5c3p0b2Yua296bG93c2tpQGxpbmFyby5vcmc+wsGUBBMBCgA+FiEE
 m9B+DgxR+NWWd7dUG5NDfTtBYpsFAmI+BxMCGwMFCRRfreEFCwkIBwIGFQoJCAsCBBYCAwEC
 HgECF4AACgkQG5NDfTtBYptgbhAAjAGunRoOTduBeC7V6GGOQMYIT5n3OuDSzG1oZyM4kyvO
 XeodvvYv49/ng473E8ZFhXfrre+c1olbr1A8pnz9vKVQs9JGVa6wwr/6ddH7/yvcaCQnHRPK
 mnXyP2BViBlyDWQ71UC3N12YCoHE2cVmfrn4JeyK/gHCvcW3hUW4i5rMd5M5WZAeiJj3rvYh
 v8WMKDJOtZFXxwaYGbvFJNDdvdTHc2x2fGaWwmXMJn2xs1ZyFAeHQvrp49mS6PBQZzcx0XL5
 cU9ZjhzOZDn6Apv45/C/lUJvPc3lo/pr5cmlOvPq1AsP6/xRXsEFX/SdvdxJ8w9KtGaxdJuf
 rpzLQ8Ht+H0lY2On1duYhmro8WglOypHy+TusYrDEry2qDNlc/bApQKtd9uqyDZ+rx8bGxyY
 qBP6bvsQx5YACI4p8R0J43tSqWwJTP/R5oPRQW2O1Ye1DEcdeyzZfifrQz58aoZrVQq+innR
 aDwu8qDB5UgmMQ7cjDSeAQABdghq7pqrA4P8lkA7qTG+aw8Z21OoAyZdUNm8NWJoQy8m4nUP
 gmeeQPRc0vjp5JkYPgTqwf08cluqO6vQuYL2YmwVBIbO7cE7LNGkPDA3RYMu+zPY9UUi/ln5
 dcKuEStFZ5eqVyqVoZ9eu3RTCGIXAHe1NcfcMT9HT0DPp3+ieTxFx6RjY3kYTGLOwU0EVUNc
 NAEQAM2StBhJERQvgPcbCzjokShn0cRA4q2SvCOvOXD+0KapXMRFE+/PZeDyfv4dEKuCqeh0
 hihSHlaxTzg3TcqUu54w2xYskG8Fq5tg3gm4kh1Gvh1LijIXX99ABA8eHxOGmLPRIBkXHqJY
 oHtCvPc6sYKNM9xbp6I4yF56xVLmHGJ61KaWKf5KKWYgA9kfHufbja7qR0c6H79LIsiYqf92
 H1HNq1WlQpu/fh4/XAAaV1axHFt/dY/2kU05tLMj8GjeQDz1fHas7augL4argt4e+jum3Nwt
 yupodQBxncKAUbzwKcDrPqUFmfRbJ7ARw8491xQHZDsP82JRj4cOJX32sBg8nO2N5OsFJOcd
 5IE9v6qfllkZDAh1Rb1h6DFYq9dcdPAHl4zOj9EHq99/CpyccOh7SrtWDNFFknCmLpowhct9
 5ZnlavBrDbOV0W47gO33WkXMFI4il4y1+Bv89979rVYn8aBohEgET41SpyQz7fMkcaZU+ok/
 +HYjC/qfDxT7tjKXqBQEscVODaFicsUkjheOD4BfWEcVUqa+XdUEciwG/SgNyxBZepj41oVq
 FPSVE+Ni2tNrW/e16b8mgXNngHSnbsr6pAIXZH3qFW+4TKPMGZ2rZ6zITrMip+12jgw4mGjy
 5y06JZvA02rZT2k9aa7i9dUUFggaanI09jNGbRA/ABEBAAHCwXwEGAEKACYCGwwWIQSb0H4O
 DFH41ZZ3t1Qbk0N9O0FimwUCYDzvagUJFF+UtgAKCRAbk0N9O0Fim9JzD/0auoGtUu4mgnna
 oEEpQEOjgT7l9TVuO3Qa/SeH+E0m55y5Fjpp6ZToc481za3xAcxK/BtIX5Wn1mQ6+szfrJQ6
 59y2io437BeuWIRjQniSxHz1kgtFECiV30yHRgOoQlzUea7FgsnuWdstgfWi6LxstswEzxLZ
 Sj1EqpXYZE4uLjh6dW292sO+j4LEqPYr53hyV4I2LPmptPE9Rb9yCTAbSUlzgjiyyjuXhcwM
 qf3lzsm02y7Ooq+ERVKiJzlvLd9tSe4jRx6Z6LMXhB21fa5DGs/tHAcUF35hSJrvMJzPT/+u
 /oVmYDFZkbLlqs2XpWaVCo2jv8+iHxZZ9FL7F6AHFzqEFdqGnJQqmEApiRqH6b4jRBOgJ+cY
 qc+rJggwMQcJL9F+oDm3wX47nr6jIsEB5ZftdybIzpMZ5V9v45lUwmdnMrSzZVgC4jRGXzsU
 EViBQt2CopXtHtYfPAO5nAkIvKSNp3jmGxZw4aTc5xoAZBLo0OV+Ezo71pg3AYvq0a3/oGRG
 KQ06ztUMRrj8eVtpImjsWCd0bDWRaaR4vqhCHvAG9iWXZu4qh3ipie2Y0oSJygcZT7H3UZxq
 fyYKiqEmRuqsvv6dcbblD8ZLkz1EVZL6djImH5zc5x8qpVxlA0A0i23v5QvN00m6G9NFF0Le
 D2GYIS41Kv4Isx2dEFh+/Q==
In-Reply-To: <ZVTgfzeK6GkKpArK@xhacker>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 15/11/2023 16:15, Jisheng Zhang wrote:
> On Wed, Nov 15, 2023 at 03:02:21PM +0000, Conor Dooley wrote:
>> On Wed, Nov 15, 2023 at 09:56:07AM -0500, Samuel Holland wrote:
>>> On 2023-11-15 7:27 AM, Jisheng Zhang wrote:
>>>> On Tue, Nov 14, 2023 at 10:12:35PM +0100, Krzysztof Kozlowski wrote:
>>>>> On 13/11/2023 01:55, Jisheng Zhang wrote:
>>>>> ...
>>>>>
>>>>>> diff --git a/include/dt-bindings/reset/sophgo,cv1800b-reset.h b/include/dt-bindings/reset/sophgo,cv1800b-reset.h
>>>>>> new file mode 100644
>>>>>> index 000000000000..28dda71369b4
>>>>>> --- /dev/null
>>>>>> +++ b/include/dt-bindings/reset/sophgo,cv1800b-reset.h
>>>>>> @@ -0,0 +1,96 @@
>>>>>> +/* SPDX-License-Identifier: GPL-2.0 OR MIT */
>>>>>> +/*
>>>>>> + * Copyright (C) 2023 Sophgo Technology Inc. All rights reserved.
>>>>>> + * Copyright (C) 2023 Jisheng Zhang <jszhang@kernel.org>
>>>>>> + */
>>>>>> +
>>>>>> +#ifndef _DT_BINDINGS_CV1800B_RESET_H
>>>>>> +#define _DT_BINDINGS_CV1800B_RESET_H
>>>>>> +
>>>>>> +/*				0-1	*/
>>>>>> +#define RST_DDR			2
>>>>>> +#define RST_H264C		3
>>>>>> +#define RST_JPEG		4
>>>>>> +#define RST_H265C		5
>>>>>> +#define RST_VIPSYS		6
>>>>>> +#define RST_TDMA		7
>>>>>> +#define RST_TPU			8
>>>>>> +#define RST_TPUSYS		9
>>>>>> +/*				10	*/
>>>>>
>>>>> Why do you have empty IDs? IDs start at 0 and are incremented by 1.
>>>>
>>>> there's 1:1 mapping between the ID and bit. Some bits are reserved, I.E
>>>> no actions at all. Is "ID start at 0 and increment by 1" documented
>>>> in some docs? From another side, I also notice some SoCs especially
>>>> those which make use of reset-simple driver don't strictly follow
>>>> this rule, for example, amlogic,meson-a1-reset.h and so on. What
>>>> happened?
>>>>
>>>> And I'd like to ask a question here before cooking 2nd version:
>>>> if the HW programming logic is the same as reset-simple, but some
>>>> or many bits are reserved, what's the can-be-accepted way to support
>>>> the reset controller? Use reset-simple? Obviously if we want the
>>>> "ID start at 0 and increment by 1" rule, then we have to write
>>>> a custom driver which almost use the reset-simple but with a
>>>> customized mapping.
>>>
>>> There are two possible situations. Either the reset specifier maps directly to
>>> something in the hardware, or you are inventing some brand new enumeration to
>>> use as a specifier.
>>>
>>> In the first situation, you do not need a header. We assume the user will look
>>> to the SoC documentation if they want to know what the numbers mean. (You aren't
>>> _creating_ an ABI, since the ABI is already defined by the hardware.)
>>>
>>> In the second situation, since we are inventing something new, the numbers
>>> should be contiguous. This is what Krzysztof's comment was about.
>>>
>>> For this reset device, the numbers are hardware bit offsets, so you are in the
>>> first situation. So I think the recommended solution here is to remove the
>>> header entirely and use the bit numbers directly in the SoC devicetree.
>>>
>>> It's still appropriate to use reset-simple. Adding some new mapping would make
>>> things more complicated for no benefit.
>>
>> Further, I think it is fine in that case to have a header, just the
>> header doesn't belong as a binding, and can instead go in the dts
>> directory.
> 
> Hi Samuel, Conor,
> 
> thanks a lot for the suggestion!

There is actually a thing here I missed. If this is a reset-simple
driver with dedicated SoC-specific compatible, you could want to have a
binding header to have IDs. This way later you can easily replace the
driver with another implementation, which does no rely on 1-1 mapping to
reset bits.

Therefore the reset-simple could be the exception where reset-bits could
have a meaning as binding header.

Best regards,
Krzysztof