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

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Date:   Mon, 6 Aug 2018 15:05:27 +0800
From:   "Wu, Songjun" <songjun.wu@...ux.intel.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     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,
        "open list:RALINK MIPS ARCHITECTURE" <linux-mips@...ux-mips.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-serial@...r.kernel.org, DTML <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 8/5/2018 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