linux-kernel - Re: [PATCH v2 14/18] serial: intel: Add CCF support

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Message-ID: <d6d0be20-aea9-cecf-1e39-3d65c0dbad5f@linux.intel.com>
Date:   Tue, 7 Aug 2018 15:18:45 +0800
From:   "Wu, Songjun" <songjun.wu@...ux.intel.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Hauke Mehrtens <hauke@...ke-m.de>, hua.ma@...ux.intel.com,
        yixin.zhu@...ux.intel.com, chuanhua.lei@...ux.intel.com,
        qi-ming.wu@...el.com,
        Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jiri Slaby <jslaby@...e.com>
Subject: Re: [PATCH v2 14/18] serial: intel: Add CCF support



On 8/6/2018 5:29 PM, Geert Uytterhoeven wrote:
> Hi Songjun,
>
> On Mon, Aug 6, 2018 at 10:58 AM Wu, Songjun <songjun.wu@...ux.intel.com> wrote:
>> On 8/6/2018 3:20 PM, Geert Uytterhoeven wrote:
>>> On Mon, Aug 6, 2018 at 9:15 AM Wu, Songjun <songjun.wu@...ux.intel.com> wrote:
>>>> On 8/5/2018 5:03 AM, Arnd Bergmann wrote:
>>>>> On Sat, Aug 4, 2018 at 2:43 PM, Greg Kroah-Hartman
>>>>> <gregkh@...uxfoundation.org> wrote:
>>>>>> On Sat, Aug 04, 2018 at 12:54:22PM +0200, Hauke Mehrtens wrote:
>>>>>>> On 08/03/2018 12:30 PM, Greg Kroah-Hartman wrote:
>>>>>>>> On Fri, Aug 03, 2018 at 03:33:38PM +0800, Wu, Songjun wrote:
>>>>>>> This patch makes it possible to use it with the legacy lantiq code and
>>>>>>> also with the common clock framework. I see multiple options to fix this
>>>>>>> problem.
>>>>>>>
>>>>>>> 1. The current approach to have it as a compile variant for a) legacy
>>>>>>> lantiq arch code without common clock framework and b) support for SoCs
>>>>>>> using the common clock framework.
>>>>>>> 2. Convert the lantiq arch code to the common clock framework. This
>>>>>>> would be a good approach, but it need some efforts.
>>>>>>> 3. Remove the arch/mips/lantiq code. There are still users of this code.
>>>>>>> 4. Use the old APIs also for the new xRX500 SoC, I do not like this
>>>>>>> approach.
>>>>>>> 5. Move lantiq_soc.h to somewhere in include/linux/ so it is globally
>>>>>>> available and provide some better wrapper code.
>>>>>> I don't really care what you do at this point in time, but you all
>>>>>> should know better than the crazy #ifdef is not allowed to try to
>>>>>> prevent/allow the inclusion of a .h file.  Checkpatch might have even
>>>>>> warned you about it, right?
>>>>>>
>>>>>> So do it correctly, odds are #5 is correct, as that makes it work like
>>>>>> any other device in the kernel.  You are not unique here.
>>>>> The best approach here would clearly be 2. We don't want platform
>>>>> specific header files for doing things that should be completely generic.
>>>>>
>>>>> Converting lantiq to the common-clk framework obviously requires
>>>>> some work, but then again the whole arch/mips/lantiq/clk.c file
>>>>> is fairly short and maybe not that hard to convert.
>>>>>
>>>>> >From looking at arch/mips/lantiq/xway/sysctrl.c, it appears that you
>>>>> already use the clkdev lookup mechanism for some devices without
>>>>> using COMMON_CLK, so I would assume that you can also use those
>>>>> for the remaining clks, which would be much simpler. It registers
>>>>> one anonymous clk there as
>>>>>
>>>>>            clkdev_add_pmu("1e100c00.serial", NULL, 0, 0, PMU_ASC1);
>>>>>
>>>>> so why not add replace that with two named clocks and just use
>>>>> the same names in the DT for the newer chip?
>>>>>
>>>>>          Arnd
>>>> We discussed internally and have another solution for this issue.
>>>> Add one lantiq.h in the serial folder, and use "#ifdef preprocessor" in
>>>> lantiq.h,
>>>> also providing no-op stub functions in the #else case, then call those
>>>> functions
>>>> unconditionally from lantiq.c to avoid #ifdef in C file.
>>>>
>>>> To support CCF in legacy product is another topic, is not included in
>>>> this patch.
>>>>
>>>> The implementation is as following：
>>>> #ifdef CONFIG_LANTIQ
>>>> #include <lantiq_soc.h>
>>>> #else
>>>> #define LTQ_EARLY_ASC 0
>>>> #define CPHYSADDR(_val) 0
>>>>
>>>> static inline struct clk *clk_get_fpi(void)
>>>> {
>>>>        return NULL;
>>>> }
>>>> #endif
>>> Why not use clkdev_add(), as Arnd suggested?
>>> That would be a 3-line patch without introducing a new header file and an ugly
>>> #ifdef, which complicates compile coverage testing?
>>>
>> The reason we add a new head file is also for two macros(LTQ_EARLY_ASC
>> and CPHYSADDR)
>> used by legacy product. We need to provide the no-op stub for these two
>> macro for new product.
> No you don't. The line number should not be obtained by comparing the
> resource address with a hardcoded base address.
This is the previous code. Now the line number is obtained from dts.
We keep this code for the compatibility.

Referring to the conditional-compilation part in coding-style,
We add a header file to avoid using “#ifdef” in C file.
> Perhaps the override of port->line should just be removed, as IIRC, the serial
> core has already filled in that field with the (next available) line number?
>
> Gr{oetje,eeting}s,
>
>                          Geert