linux-kernel - Re: [PATCH next v9 1/4] i2c: hisi: Add initial device tree support

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Date:   Mon, 31 Oct 2022 17:42:18 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     chenweilong <chenweilong@...wei.com>
Cc:     yangyicong@...ilicon.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, wsa@...nel.org,
        f.fainelli@...il.com, jarkko.nikula@...ux.intel.com,
        jdelvare@...e.de, william.zhang@...adcom.com, jsd@...ihalf.com,
        conor.dooley@...rochip.com, phil.edworthy@...esas.com,
        tharunkumar.pasumarthi@...rochip.com, semen.protsenko@...aro.org,
        kfting@...oton.com, linux-i2c@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH next v9 1/4] i2c: hisi: Add initial device tree support

On Mon, Oct 31, 2022 at 09:57:51AM +0800, chenweilong wrote:
> On 2022/10/31 6:01, Andy Shevchenko wrote:
> > On Sat, Oct 29, 2022 at 07:59:36PM +0800, Weilong Chen wrote:
> >> The HiSilicon I2C controller can be used on embedded platform, which
> >> boot from devicetree.
> > ...
> >
> >> +#include <linux/acpi.h>
> >> +#include <linux/of.h>
> > Why?
> >
> > ...
> >
> >> +#ifdef CONFIG_ACPI
> > Why?
> >
> > ...
> >
> >> +#ifdef CONFIG_OF
> > Why?
> >
> > ...
> >
> >> -		.acpi_match_table = hisi_i2c_acpi_ids,
> >> +		.acpi_match_table = ACPI_PTR(hisi_i2c_acpi_ids),
> > Why?
> >
> > ...
> >
> >> +		.of_match_table = of_match_ptr(hisi_i2c_dts_ids),
> > Why of_match_ptr()?
> 
> There's a lot of drivers use of_match_ptr/ACPI_PTR to protect the of_device_id and
> have explicit headers file references to linux/acpi.h or linux/of.h, such as
> drivers/media/platform/intel/pxa_camera.c,
> bluetooth/hci_intel.c, 
> platform/x86/intel/chtwc_int33fe.c,
> platform/x86/intel/pmc/core.c and so on.

We have a lot of the legacy or not-up-to-dated to all new kernel APIs code.
Does it justify not to use the new approach in the new contribution?

...

> The acpi.h and of.h have a nice function or macro definition if CONFIG_OF/ACPI is not satisfy,
> for example:
> 
> #define ACPI_PTR(_ptr)  (_ptr)  vs  #define ACPI_PTR(_ptr)  (NULL)
> 
> and also a lot of 'static inline' function there.

And why do you need it?

...

> Seems a good idea to remove all of them, the codes your noted may look a bit
> verbose there. But I think it is valuable for a driver and device ,telling
> users it support acpi boot or is it just embedded.

So, what do we gain here?

(Fill the "Advantages of your code" section below)

Disadvantages of your code:
- ugly ifdeffery which we usually do not appreciate
- in some cases it's good to have OF ID table on ACPI platforms (see what
  PRP0001 trick is)
- use old approach for the compiler on how to avoid warnings of the static
  variables being defined and not used (note, neither ACPI_PTR() nor
  of_match_ptr() provides a new approach on that, so you have to amend them
  first)
- as a side effect additional headers to be included that are used for 1% or
  less of their capacity and slow down the compilation

-- 
With Best Regards,
Andy Shevchenko