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Subject: Re: [PATCH v2 08/18] serial: intel: Get serial id from dts
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     hua.ma@linux.intel.com, yixin.zhu@linux.intel.com,
        chuanhua.lei@linux.intel.com, qi-ming.wu@intel.com,
        Linux MIPS Mailing List <linux-mips@linux-mips.org>,
        linux-clk <linux-clk@vger.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, Greg KH <gregkh@linuxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jiri Slaby <jslaby@suse.com>
References: <20180803030237.3366-1-songjun.wu@linux.intel.com>
 <20180803030237.3366-9-songjun.wu@linux.intel.com>
 <CAMuHMdXkGchPN337dXbBVOFsb1o-Tkh8S_z=uCm3Z0sDjPVMKA@mail.gmail.com>
 <734bddbc-a5aa-d50d-0e7b-d8adc4d1afb2@linux.intel.com>
 <CAMuHMdVgC__AJHCEKT9UhdK4Jh4bm-s0ihH8mvx7KQ7+vzh6Ag@mail.gmail.com>
From:   "Wu, Songjun" <songjun.wu@linux.intel.com>
Message-ID: <ba7e68d4-d749-1afc-8a4f-57ebee88a1fb@linux.intel.com>
Date:   Fri, 10 Aug 2018 16:13:34 +0800
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On 8/8/2018 4:33 PM, Geert Uytterhoeven wrote:
> Hi Songjun,
>
> On Wed, Aug 8, 2018 at 6:05 AM Wu, Songjun <songjun.wu@linux.intel.com> wrote:
>> On 8/7/2018 3:33 PM, Geert Uytterhoeven wrote:
>>> On Fri, Aug 3, 2018 at 5:04 AM Songjun Wu <songjun.wu@linux.intel.com> wrote:
>>>> Get serial id from dts.
>>>>
>>>> "#ifdef CONFIG_LANTIQ" preprocessor is used because LTQ_EARLY_ASC
>>>> macro is defined in lantiq_soc.h.
>>>> lantiq_soc.h is in arch path for legacy product support.
>>>>
>>>> arch/mips/include/asm/mach-lantiq/xway/lantiq_soc.h
>>>>
>>>> If "#ifdef preprocessor" is changed to
>>>> "if (IS_ENABLED(CONFIG_LANTIQ))", when CONFIG_LANTIQ is not enabled,
>>>> code using LTQ_EARLY_ASC is compiled.
>>>> Compilation will fail for no LTQ_EARLY_ASC defined.
>>>>
>>>> Signed-off-by: Songjun Wu <songjun.wu@linux.intel.com>
>>> Thanks for your patch!
>>>
>>>> @@ -699,9 +700,19 @@ lqasc_probe(struct platform_device *pdev)
>>>>                   return -ENODEV;
>>>>           }
>>>>
>>>> -       /* check if this is the console port */
>>>> -       if (mmres->start != CPHYSADDR(LTQ_EARLY_ASC))
>>>> -               line = 1;
>>>> +       /* get serial id */
>>>> +       line = of_alias_get_id(node, "serial");
>>>> +       if (line < 0) {
>>>> +#ifdef CONFIG_LANTIQ
>>>> +               if (mmres->start == CPHYSADDR(LTQ_EARLY_ASC))
>>>> +                       line = 0;
>>>> +               else
>>>> +                       line = 1;
>>>> +#else
>>>> +               dev_err(&pdev->dev, "failed to get alias id, errno %d\n", line);
>>>> +               return line;
>>> Please note that not providing a fallback here makes life harder when using
>>> DT overlays.
>>> See the description of commit 7678f4c20fa7670f ("serial: sh-sci: Add support
>>> for dynamic instances") for background info.
>> Thanks for your comment.
>> The logic in commit 7678f4c20fa7670f is not suitable here.
>> We need to know which serial instance is used for console.
>> We cannot use dynamic serial instance here.
> Why does the driver need to use which serial instance is used for the console?
> Hardcoding that is not an option, as the board DTS may specify the console using
> chosen/stdout-path.
In legacy platform in open source, it only defined asc1 in dts.
There's no asc0 in legacy dts.While in the new platform, asc0
is defined in dts. There's no asc1 in new platform dts.
To avoid hard code in driver, alias serial0 is used to unified
driver code. Actually only one serial is supported in SoC.

aliases {
         serial0 = &asc0;
};

chosen {
     bootargs = "earlycon  clk_ignore_unused";
     stdout-path = "serial0";
};