[PATCH v3 RESEND] clk: sifive: Fix W=1 kernel build warning

[Lee Jones]

On Thu, 13 Jan 2022, Jessica Clarke wrote:

> On 13 Jan 2022, at 17:21, Lee Jones <lee.jones at linaro.org> wrote:
> > 
> > On Thu, 13 Jan 2022, Zong Li wrote:
> > 
> >> On Wed, Jan 12, 2022 at 5:09 PM Lee Jones <lee.jones at linaro.org> wrote:
> >>> 
> >>> On Wed, 12 Jan 2022, Zong Li wrote:
> >>> 
> >>>> On Tue, Jan 11, 2022 at 5:32 PM Lee Jones <lee.jones at linaro.org> wrote:
> >>>>> 
> >>>>> On Tue, 11 Jan 2022, Zong Li wrote:
> >>>>> 
> >>>>>> On Mon, Jan 10, 2022 at 5:50 PM Lee Jones <lee.jones at linaro.org> wrote:
> >>>>>>> 
> >>>>>>> Please improve the subject line.
> >>>>>>> 
> >>>>>>> If this is a straight revert, the subject line should reflect that.
> >>>>>>> 
> >>>>>>> If not, you need to give us specific information regarding the purpose
> >>>>>>> of this patch.  Please read the Git log for better, more forthcoming
> >>>>>>> examples.
> >>>>>>> 
> >>>>>> 
> >>>>>> It seems to me that this patch is not a straight revert, it provides
> >>>>>> another way to fix the original build warnings, just like
> >>>>>> '487dc7bb6a0c' tried to do. I guess the commit message has described
> >>>>>> what the original warnings is and what the root cause is, it also
> >>>>>> mentioned what is changed in this patch. I'm a bit confused whether we
> >>>>>> need to add fixes tag, it looks like that it might cause some
> >>>>>> misunderstanding?
> >>>>> 
> >>>>> I think it's the patch description and subject that is causing the
> >>>>> misunderstanding.
> >>>>> 
> >>>> 
> >>>> Yes, the subject should be made better.
> >>>> 
> >>>>> Please help me with a couple of points and I'll help you draft
> >>>>> something up.
> >>>>> 
> >>>>> Firstly, what alerted you to the problem you're attempting to solve?
> >>>>> 
> >>>> 
> >>>> I recently noticed the code was changed, I guess that I was missing
> >>>> something there. After tracking the log, I found that there is a build
> >>>> warning in the original implementation, and it was already fixed, but
> >>>> it seems to me that there are still some situations there, please help
> >>>> me to see the following illustration.
> >>>> 
> >>>>>>>> --- a/drivers/clk/sifive/fu540-prci.c
> >>>>>>>> +++ b/drivers/clk/sifive/fu540-prci.c
> >>>>>>>> @@ -20,7 +20,6 @@
> >>>>>>>> 
> >>>>>>>> #include <dt-bindings/clock/sifive-fu540-prci.h>
> >>>>>>>> 
> >>>>>>>> -#include "fu540-prci.h"
> >>>>> 
> >>>>> How is this related to the issue/patch?
> >>>>> 
> >>>> 
> >>>> Let's go back to the version without '487dc7bb6a0c' fix. The
> >>>> prci_clk_fu540 variable is defined in sifive-fu540-prci.h header,
> >>>> however, fu540-prci.c includes this header but doesn't use this
> >>>> variable, so the warnings happen.
> >>>> 
> >>>> The easiest way to do it is just removing this line, then the warning
> >>>> could be fixed. But as the '487dc7bb6a0c' or this patch does, the code
> >>>> should be improved, the prci_clk_fu540 variable shouldn't be defined
> >>>> in the header, it should be moved somewhere.
> >>>> 
> >>>>>>>> +struct prci_clk_desc prci_clk_fu540 = {
> >>>>>>>> +     .clks = __prci_init_clocks_fu540,
> >>>>>>>> +     .num_clks = ARRAY_SIZE(__prci_init_clocks_fu540),
> >>>>>>>> +};
> >>>>> 
> >>>>>>>> diff --git a/drivers/clk/sifive/fu540-prci.h b/drivers/clk/sifive/fu540-prci.h
> >>>>>>>> index c220677dc010..931d6cad8c1c 100644
> >>>>>>>> --- a/drivers/clk/sifive/fu540-prci.h
> >>>>>>>> +++ b/drivers/clk/sifive/fu540-prci.h
> >>>>>>>> @@ -7,10 +7,6 @@
> >>>>>>>> +extern struct prci_clk_desc prci_clk_fu540;
> >>>>> 
> >>>>>>>> diff --git a/drivers/clk/sifive/sifive-prci.c b/drivers/clk/sifive/sifive-prci.c
> >>>>>>>> index 80a288c59e56..916d2fc28b9c 100644
> >>>>>>>> --- a/drivers/clk/sifive/sifive-prci.c
> >>>>>>>> +++ b/drivers/clk/sifive/sifive-prci.c
> >>>>>>>> @@ -12,11 +12,6 @@
> >>>>>>>> #include "fu540-prci.h"
> >>>>>>>> #include "fu740-prci.h"
> >>>>>>>> 
> >>>>>>>> -static const struct prci_clk_desc prci_clk_fu540 = {
> >>>>>>>> -     .clks = __prci_init_clocks_fu540,
> >>>>>>>> -     .num_clks = ARRAY_SIZE(__prci_init_clocks_fu540),
> >>>>>>>> -};
> >>>>>>>> -
> >>>>> 
> >>>>> I'm not sure if it's you or I that is missing the point here, but
> >>>>> prci_clk_fu540 is used within *this* file itself:
> >>>>> 
> >>>> 
> >>>> Here is another situation I mentioned at the beginning, if we'd like
> >>>> to put prci_clk_fu540 here, prci_clk_fu740 should be put here as well.
> >>>> I guess you didn't do that because there is a bug in the original
> >>>> code, fu740-prci.c misused the fu540-prci.h, so there is no build
> >>>> warning on fu740. FU740 still works correctly by misusing the
> >>>> fu540-prci.h header because fu740-prci.c doesn't actually use the
> >>>> prci_clk_fu740 variable, like fu540 we talked about earlier.
> >>>> 
> >>>>> static const struct of_device_id sifive_prci_of_match[] = {
> >>>>>         {.compatible = "sifive,fu540-c000-prci", .data = &prci_clk_fu540},
> >>>>>         {.compatible = "sifive,fu740-c000-prci", .data = &prci_clk_fu740},
> >>>>>         {}
> >>>>> };
> >>>>> 
> >>>>> So why are you moving it out to somewhere it is *not* used and making
> >>>>> it an extern?  This sounds like the opposite to what you'd want?
> >>>> 
> >>>> The idea is that sifive-prci.c is the core and common part of PRCI,
> >>>> and I'd like to separate the SoCs-dependent part into SoCs-dependent
> >>>> files, such as fu540-prci.c and fu740-prci.c. The goal is if we add
> >>>> new SoCs in the future, we can just put the SoCs-dependent data
> >>>> structure in the new C file, and do as minimum modification as
> >>>> possible in the core file (i.e. sifive-prci.c). It might also help us
> >>>> to see all SoCs-dependent data in one file, then we don't need to
> >>>> cross many files. Putting these two variables in sifive-pric.c is the
> >>>> right thing to do, but that is why I separate them and make them
> >>>> extern in this patch.
> >>> 
> >>> I can see what you are doing, but I don't think this is the right
> >>> thing to do.  Please put the struct in the same location as it's
> >>> referenced.
> >> 
> >> If we decide to move them into sifive-prci.c (i.e. put it in where
> >> it's referenced.), I worried that we might need to move all stuff
> >> which are in fu540-prci.c and fu740-prci.c. Because 'prci_clk_fu540'
> >> is referenced in sifive-prci.c, whereas '__prci_init_clocks_fu540' is
> >> used by 'prci_clk_fu540', and the almost things in fu540-prci.c are
> >> used by '__prci_init_clocks_fu540'. It seems to be a little bit
> >> difficult to clearly decouple it for modularization which I want to
> >> do. What this patch does might be a accepted way, I hope that you can
> >> consider it again.
> >> 
> >>> 
> >>> And yes that should also be the case for prci_clk_fu740 and yes, it
> >>> was over-looked because it wasn't causing warnings at build time for
> >>> whatever reason.
> >>> 
> >>> IMHO, placing 'struct of_device_id' match tables in headers is also
> >>> odd and is likely the real cause of this strange situation.
> >> 
> >> I couldn't see what are you pointing, do you mind give more details
> >> about it? It seems to me that the match table is put in C file (i.e.
> >> sifive-prci.c).
> > 
> > Oh, sorry, it's a common source file, rather than a header.
> > 
> > Okay, so I went and actually looked at the code this time.
> > 
> > If I were you I would move all of the device specific structs and
> > tables into the device specific header files, then delete the device
> > specific source (C) files entirely.
> > 
> > There seems to be no good reason for carrying a common source file as
> > well as a source file AND header file for each supported device.
> > IMHO, that's over-complicating things for no apparent gain.
> 
> The reason it exists the way it does is that the driver uses the header
> files shipped and used for the device tree bindings, and they give the
> same names to different constants (the first three constants are in
> fact the same so don’t clash, but PRCI_CLK_TLCLK is different between
> the two), so can’t both be in the same translation unit (at least not
> without some gross #undef’ing). In FreeBSD I took the alternate
> approach of just defining our own FU540_ and FU740_ namespaced copies
> of the constants, as drivers do for most things anyway.

That's a sensible approach.

One which we use in Linux extensively.

-- 
Lee Jones [李琼斯]
Principal Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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