[PATCH] staging: fbtft: fix coding style issue in fbtft-bus.c

[PATCH] staging: fbtft: fix coding style issue in fbtft-bus.c

[Baker]

Remove trailing space and comma before closing parenthesis ')' in
define_fbtft_write_reg macro as reported by checkpatch.pl.

Signed-off-by: Baker <mzndmzn@gmail.com>
---
 drivers/staging/fbtft/fbtft-bus.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/fbtft/fbtft-bus.c b/drivers/staging/fbtft/fbtft-bus.c
index 30e436ff19e4..409770891c54 100644
--- a/drivers/staging/fbtft/fbtft-bus.c
+++ b/drivers/staging/fbtft/fbtft-bus.c
@@ -62,9 +62,9 @@ out:									      \
 }                                                                             \
 EXPORT_SYMBOL(func);
 
-define_fbtft_write_reg(fbtft_write_reg8_bus8, u8, u8, )
+define_fbtft_write_reg(fbtft_write_reg8_bus8, u8, u8)
 define_fbtft_write_reg(fbtft_write_reg16_bus8, __be16, u16, cpu_to_be16)
-define_fbtft_write_reg(fbtft_write_reg16_bus16, u16, u16, )
+define_fbtft_write_reg(fbtft_write_reg16_bus16, u16, u16)
 
 void fbtft_write_reg8_bus9(struct fbtft_par *par, int len, ...)
 {
-- 
2.47.3

[PATCH v3] staging: fbtft: replace empty macro args with identity converter

[Baker]

The define_fbtft_write_reg macro calls 'modifier' as a function.
Passing an empty token as modifier is undefined behavior in C for
fixed-arity macros. Introduce fbtft_no_conv() as an identity
function to replace the empty args in the no-conversion cases.

Signed-off-by: Baker <mzndmzn@gmail.com>
---
 drivers/staging/fbtft/fbtft-bus.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/fbtft/fbtft-bus.c b/drivers/staging/fbtft/fbtft-bus.c
index 30e436ff19e4..7f3fd30576ab 100644
--- a/drivers/staging/fbtft/fbtft-bus.c
+++ b/drivers/staging/fbtft/fbtft-bus.c
@@ -11,6 +11,8 @@
  *
  *****************************************************************************/
 
+#define fbtft_no_conv(x) (x)
+
 #define define_fbtft_write_reg(func, buffer_type, data_type, modifier)        \
 void func(struct fbtft_par *par, int len, ...)                                \
 {                                                                             \
@@ -62,9 +64,9 @@ out:									      \
 }                                                                             \
 EXPORT_SYMBOL(func);
 
-define_fbtft_write_reg(fbtft_write_reg8_bus8, u8, u8, )
+define_fbtft_write_reg(fbtft_write_reg8_bus8, u8, u8, fbtft_no_conv)
 define_fbtft_write_reg(fbtft_write_reg16_bus8, __be16, u16, cpu_to_be16)
-define_fbtft_write_reg(fbtft_write_reg16_bus16, u16, u16, )
+define_fbtft_write_reg(fbtft_write_reg16_bus16, u16, u16, fbtft_no_conv)
 
 void fbtft_write_reg8_bus9(struct fbtft_par *par, int len, ...)
 {
-- 
2.47.3

Re: [PATCH v3] staging: fbtft: replace empty macro args with identity converter

[Andy Shevchenko]

On Sun, Apr 12, 2026 at 8:33 PM Baker <mzndmzn@gmail.com> wrote:
>
> The define_fbtft_write_reg macro calls 'modifier' as a function.
> Passing an empty token as modifier is undefined behavior in C for
> fixed-arity macros. Introduce fbtft_no_conv() as an identity
> function to replace the empty args in the no-conversion cases.

This trick is used in the kernel (usually for u8). If you really want
to improve, use _Generic() instead.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v3] staging: fbtft: replace empty macro args with identity converter

[Greg KH]

On Mon, Apr 13, 2026 at 08:58:50AM +0300, Andy Shevchenko wrote:
> On Sun, Apr 12, 2026 at 8:33 PM Baker <mzndmzn@gmail.com> wrote:
> >
> > The define_fbtft_write_reg macro calls 'modifier' as a function.
> > Passing an empty token as modifier is undefined behavior in C for
> > fixed-arity macros. Introduce fbtft_no_conv() as an identity
> > function to replace the empty args in the no-conversion cases.
> 
> This trick is used in the kernel (usually for u8). If you really want
> to improve, use _Generic() instead.

No, sorry, this code is fine as-is.

greg k-h

Re: [PATCH v3] staging: fbtft: replace empty macro args with identity converter

[Andy Shevchenko]

On Mon, Apr 13, 2026 at 9:03 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> On Mon, Apr 13, 2026 at 08:58:50AM +0300, Andy Shevchenko wrote:
> > On Sun, Apr 12, 2026 at 8:33 PM Baker <mzndmzn@gmail.com> wrote:
> > >
> > > The define_fbtft_write_reg macro calls 'modifier' as a function.
> > > Passing an empty token as modifier is undefined behavior in C for
> > > fixed-arity macros. Introduce fbtft_no_conv() as an identity
> > > function to replace the empty args in the no-conversion cases.
> >
> > This trick is used in the kernel (usually for u8). If you really want
> > to improve, use _Generic() instead.
>
> No, sorry, this code is fine as-is.

Works for me. I suggested they explore the possibilities, it might be
helpful somewhere else in case of the similar requirements (like in a
new code).

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] staging: fbtft: fix coding style issue in fbtft-bus.c

[kernel test robot]

Hi Baker,

kernel test robot noticed the following build errors:

[auto build test ERROR on staging/staging-testing]

url:    https://github.com/intel-lab-lkp/linux/commits/Baker/staging-fbtft-fix-coding-style-issue-in-fbtft-bus-c/20260414-101811
base:   staging/staging-testing
patch link:    https://lore.kernel.org/r/20260412173317.3329-1-mzndmzn%40gmail.com
patch subject: [PATCH] staging: fbtft: fix coding style issue in fbtft-bus.c
config: arm-randconfig-r072-20260414 (https://download.01.org/0day-ci/archive/20260414/202604141939.LhzKrfey-lkp@intel.com/config)
compiler: arm-linux-gnueabi-gcc (GCC) 13.4.0
smatch: v0.5.0-9007-gcf3ea02b
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260414/202604141939.LhzKrfey-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202604141939.LhzKrfey-lkp@intel.com/

All errors (new ones prefixed by >>):

>> drivers/staging/fbtft/fbtft-bus.c:65:53: error: macro "define_fbtft_write_reg" requires 4 arguments, but only 3 given
      65 | define_fbtft_write_reg(fbtft_write_reg8_bus8, u8, u8)
         |                                                     ^
   drivers/staging/fbtft/fbtft-bus.c:14: note: macro "define_fbtft_write_reg" defined here
      14 | #define define_fbtft_write_reg(func, buffer_type, data_type, modifier)        \
         | 
>> drivers/staging/fbtft/fbtft-bus.c:65:23: error: expected ';' before 'void'
      65 | define_fbtft_write_reg(fbtft_write_reg8_bus8, u8, u8)
         |                       ^
         |                       ;
   drivers/staging/fbtft/fbtft-bus.c:67:57: error: macro "define_fbtft_write_reg" requires 4 arguments, but only 3 given
      67 | define_fbtft_write_reg(fbtft_write_reg16_bus16, u16, u16)
         |                                                         ^
   drivers/staging/fbtft/fbtft-bus.c:14: note: macro "define_fbtft_write_reg" defined here
      14 | #define define_fbtft_write_reg(func, buffer_type, data_type, modifier)        \
         | 
   drivers/staging/fbtft/fbtft-bus.c:67:23: error: expected ';' before 'void'
      67 | define_fbtft_write_reg(fbtft_write_reg16_bus16, u16, u16)
         |                       ^
         |                       ;
      68 | 
      69 | void fbtft_write_reg8_bus9(struct fbtft_par *par, int len, ...)
         | ~~~~                   


vim +/define_fbtft_write_reg +65 drivers/staging/fbtft/fbtft-bus.c

    64	
  > 65	define_fbtft_write_reg(fbtft_write_reg8_bus8, u8, u8)
    66	define_fbtft_write_reg(fbtft_write_reg16_bus8, __be16, u16, cpu_to_be16)
    67	define_fbtft_write_reg(fbtft_write_reg16_bus16, u16, u16)
    68	

-- 
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https://github.com/intel/lkp-tests/wiki