[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

Claude review: staging: fbtft: fix coding style issue in fbtft-bus.c

[Claude Code Review Bot]

Overall Series Review

Subject: staging: fbtft: fix coding style issue in fbtft-bus.c
Author: Baker <mzndmzn@gmail.com>
Patches: 1
Reviewed: 2026-04-13T18:59:36.948669

---

**NAK — This patch is incorrect and will break compilation.**

This is a single-patch "series" that attempts to fix a checkpatch.pl style warning by removing the trailing comma and empty 4th argument from two `define_fbtft_write_reg` macro invocations. However, the empty 4th argument is **intentional and functional** — it is not a style issue. Removing it changes the macro call from 4 arguments to 3, which will cause a preprocessor error since the macro is defined with exactly 4 parameters.

---
Generated by Claude Code Patch Reviewer

Claude review: staging: fbtft: fix coding style issue in fbtft-bus.c

[Claude Code Review Bot]

Patch Review

**Result: NAK — introduces a build break**

The macro `define_fbtft_write_reg` is defined at `fbtft-bus.c:14` with **4 parameters**:

```c
#define define_fbtft_write_reg(func, buffer_type, data_type, modifier)
```

The `modifier` parameter is used throughout the macro body as a function-like call, e.g. at line 42:

```c
*buf = modifier((data_type)va_arg(args, unsigned int));
```

When the 4th argument is left **empty** (as in the original code):

```c
define_fbtft_write_reg(fbtft_write_reg8_bus8, u8, u8, )
```

the preprocessor expands `modifier((data_type)va_arg(args, unsigned int))` to simply `((u8)va_arg(args, unsigned int))` — an identity operation wrapped in parentheses. This is a deliberate and well-known C preprocessor idiom for a "no-op modifier." Compare with line 66 where `cpu_to_be16` is passed as the modifier to perform byte-swapping:

```c
define_fbtft_write_reg(fbtft_write_reg16_bus8, __be16, u16, cpu_to_be16)
```

The patch changes the invocations to only pass 3 arguments:

```c
-define_fbtft_write_reg(fbtft_write_reg8_bus8, u8, u8, )
+define_fbtft_write_reg(fbtft_write_reg8_bus8, u8, u8)
```

This will produce a compilation error like:

> `error: macro "define_fbtft_write_reg" requires 4 arguments, but only 3 given`

The trailing comma before `)` is **not** a coding style issue — it is syntactically required to pass an empty 4th macro argument. checkpatch.pl's warning is a false positive in this context.

**If the author wishes to make this cleaner**, the correct approach would be to refactor the macro itself, for example by introducing a separate 3-parameter version without `modifier`, or by using variadic macros (`__VA_ARGS__`), or by defining a no-op modifier macro like `#define IDENTITY(x) (x)` and passing that instead of an empty argument. Simply dropping the argument is not valid.

---
Generated by Claude Code Patch Reviewer

[PATCH] 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..8ce263f68ed2 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)
 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] 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

Claude review: staging: fbtft: fix coding style issue in fbtft-bus.c

[Claude Code Review Bot]

Patch Review

**Commit message:**
> 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 patch appears to be a v2/improvement over Patch 1, attempting to address the underlying concern properly by introducing an identity macro:

```c
+#define fbtft_no_conv(x) (x)
```

**However, the patch has two bugs:**

1. **Same compilation failure as Patch 1.** The invocations are still changed to 3 arguments:
   ```c
   -define_fbtft_write_reg(fbtft_write_reg8_bus8, u8, u8, )
   +define_fbtft_write_reg(fbtft_write_reg8_bus8, u8, u8)
   ```
   The `fbtft_no_conv` macro is defined but never actually passed as the 4th argument. The correct change should have been:
   ```c
   +define_fbtft_write_reg(fbtft_write_reg8_bus8, u8, u8, fbtft_no_conv)
   +define_fbtft_write_reg(fbtft_write_reg16_bus16, u16, u16, fbtft_no_conv)
   ```

2. **Incorrect premise.** The commit message claims "Passing an empty token as modifier is undefined behavior in C for fixed-arity macros." This is not true under C99+. Empty macro arguments are explicitly permitted by the C99 standard and later, and the Linux kernel builds with GNU C11. The existing code is well-defined.

**If the author wants to improve clarity** (replacing the empty argument with a named identity macro is arguably more readable, even if the empty arg is valid), the corrected version of this patch would be:

```c
#define fbtft_no_conv(x) (x)
...
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, fbtft_no_conv)
```

The commit message should also be updated to remove the UB claim and instead frame it as a readability/clarity improvement.

**Verdict:** NAK. Introduces a build failure and adds dead code (`fbtft_no_conv` defined but unused). The approach has merit if implemented correctly, but as submitted this does not compile.

---
Generated by Claude Code Patch Reviewer