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

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Message-ID: <CAJM55Z8WDcjRER3ffnj+6V=QWEmudZyaO9z2iPUvreU1okq27A@mail.gmail.com>
Date:   Fri, 15 Sep 2023 03:23:36 -0700
From:   Emil Renner Berthing <emil.renner.berthing@...onical.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Emil Renner Berthing <emil.renner.berthing@...onical.com>,
        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

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.

/Emil