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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Mon, 6 Aug 2018 11:29:51 +0200
Message-ID: <CAMuHMdUJ8-bveoHWOetjrHtq2HNPnf00PidQwJ-kZD2o86KLMw@mail.gmail.com>
Subject: Re: [PATCH v2 14/18] serial: intel: Add CCF support
To:     songjun.wu@linux.intel.com
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Greg KH <gregkh@linuxfoundation.org>,
        Hauke Mehrtens <hauke@hauke-m.de>, 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>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jiri Slaby <jslaby@suse.com>
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Hi Songjun,

On Mon, Aug 6, 2018 at 10:58 AM Wu, Songjun <songjun.wu@linux.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@linux.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@linuxfoundation.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.

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

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds