linux-kernel - Re: [PATCH 10/12] serial: 8250

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Message-ID: <0bd1742c-fa39-4f63-a594-6d325dc6b062@codethink.co.uk>
Date:   Fri, 22 Sep 2023 10:53:00 +0100
From:   Ben Dooks <ben.dooks@...ethink.co.uk>
To:     Emil Renner Berthing <emil.renner.berthing@...onical.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Wang Chen <unicornxw@...il.com>,
        linux-riscv@...ts.infradead.org, conor@...nel.org,
        aou@...s.berkeley.edu, krzysztof.kozlowski+dt@...aro.org,
        palmer@...belt.com, paul.walmsley@...ive.com, robh+dt@...nel.org
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        jszhang@...nel.org, guoren@...nel.org, chao.wei@...hgo.com,
        xiaoguang.xing@...hgo.com
Subject: Re: [PATCH 10/12] serial: 8250_dw: Add Sophgo SG2042 support

On 15/09/2023 11:23, Emil Renner Berthing wrote:
> Krzysztof Kozlowski wrote:
>> On 15/09/2023 12:02, Emil Renner Berthing wrote:
>>> Krzysztof Kozlowski wrote:
>>>> On 15/09/2023 09:25, Wang Chen wrote:
>>>>> From: Emil Renner Berthing <emil.renner.berthing@...onical.com>
>>>>>
>>>>> Add quirk to skip setting the input clock rate for the uarts on the
>>>>> Sophgo SG2042 SoC similar to the StarFive JH7100.
>>>>>
>>>>> Signed-off-by: Emil Renner Berthing <emil.renner.berthing@...onical.com>
>>>>
>>>> Missing SoB.
>>>>
>>>>> ---
>>>>>   drivers/tty/serial/8250/8250_dw.c | 5 +++--
>>>>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
>>>>> index f4cafca1a7da..6c344877a07f 100644
>>>>> --- a/drivers/tty/serial/8250/8250_dw.c
>>>>> +++ b/drivers/tty/serial/8250/8250_dw.c
>>>>> @@ -770,7 +770,7 @@ static const struct dw8250_platform_data dw8250_renesas_rzn1_data = {
>>>>>   	.quirks = DW_UART_QUIRK_IS_DMA_FC,
>>>>>   };
>>>>>
>>>>> -static const struct dw8250_platform_data dw8250_starfive_jh7100_data = {
>>>>> +static const struct dw8250_platform_data dw8250_skip_set_rate_data = {
>>>>
>>>> Why? What is wrong with old name?
>>>>
>>>>>   	.usr_reg = DW_UART_USR,
>>>>>   	.quirks = DW_UART_QUIRK_SKIP_SET_RATE,
>>>>>   };
>>>>> @@ -780,7 +780,8 @@ static const struct of_device_id dw8250_of_match[] = {
>>>>>   	{ .compatible = "cavium,octeon-3860-uart", .data = &dw8250_octeon_3860_data },
>>>>>   	{ .compatible = "marvell,armada-38x-uart", .data = &dw8250_armada_38x_data },
>>>>>   	{ .compatible = "renesas,rzn1-uart", .data = &dw8250_renesas_rzn1_data },
>>>>> -	{ .compatible = "starfive,jh7100-uart", .data = &dw8250_starfive_jh7100_data },
>>>>> +	{ .compatible = "sophgo,sg2042-uart", .data = &dw8250_skip_set_rate_data },
>>>>> +	{ .compatible = "starfive,jh7100-uart", .data = &dw8250_skip_set_rate_data },
>>>>
>>>> So devices are fully compatible? Then use compatibility and drop this
>>>> patch entirely.
>>>
>>> I'm fine with this, but these are two different companies and SoCs that just
>>> happens to have both implemented the Designware UART with an inflexible input
>>> clock. So if fx. a real quirk is found on the JH7110 then we'd need to either
>>> change the compatible on an unrelated SoC or change compatible on the JH7110 to
>>
>> Wait, why? The compatible is still there, so you just add here proper
>> entry, if ever needed.
> 
> Sorry, I messed up my example by writing JH7110 where I meant JH7100
> 
>>> something like "starfive,jh7100-uart-with-quirk" and "starfive,jh7100-uart" will
>>> forever be a quirky way to spell "dw8250 with inflexible input clock".
>>> Is that how device trees are supposed to work?
>>
>> I don't get this part. But anyway if the blocks are really designed or
>> done independently and there is no shared part, except the DWC block,
>> then indeed the compatibility might be just a coincidence...
>>
> 
> It is. Sophgo and StarFive are not the same company. Sophgo are using RISC-V
> cores from T-Head and StarFive are using cores from SiFive. They just happen to
> both use the Designware UART in the same way.

Out of interest, what's the issue with just providing an fixed clock in
the device tree for these machines?


-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius

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