linux-kernel - Re: [PATCH v3 2/2] serial: 8250/ingenic: Add support for the JZ4750/JZ4755

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Date:   Sun, 23 Oct 2022 16:15:58 +0100
From:   Paul Cercueil <paul@...pouillou.net>
To:     Siarhei Volkau <lis8215@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org
Subject: Re: [PATCH v3 2/2] serial: 8250/ingenic: Add support for the
 JZ4750/JZ4755



Le dim. 23 oct. 2022 à 17:04:49 +0300, Siarhei Volkau 
<lis8215@...il.com> a écrit :
> вс, 23 окт. 2022 г. в 12:16, Paul Cercueil 
> <paul@...pouillou.net>:
>>  Do you have such hardware?
> 
> No
> 
>>  Don't add support for cases you can't test.
> 
> It's just a side effect of that approach.
> 
>>  For what we know - all JZ475x use a 24 MHz crystal and all JZ4760(B)
>>  use a 12 MHz crystal, until proven otherwise.
> 
> Ouf course it just confirms the rule but I found one exception: 
> JZ4750 & 12MHz
> Link: 
> https://github.com/carlos-wong/uboot_jz4755/blob/master/include/configs/lib4750.h

Then when this board is upstreamed it will declare a 12 MHz oscillator 
in its DT, and the ingenic init code won't have to enable the /2 
divider for that particular board.

> Regarding your proposal:
> In my opinion enabling the divisor unconditionally is a bad practice,
> as it's already enabled (or not) by the bootloader, with respect to 
> the
> hardware capabilities.I think it's better to keep the driver as it is 
> than
> adding such things.

Well, I disagree. Linux should not depend on whatever the bootloader 
configures.

-Paul