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

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Message-ID: <0ab8e6e7-3cc2-8e50-b1f3-99616437f527@linux.intel.com>
Date:   Mon, 6 Aug 2018 16:58:49 +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 3:20 PM, Geert Uytterhoeven wrote:
> Hi Songjun,
>
> 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?
>
> Gr{oetje,eeting}s,
>
>                          Geert
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.