[PATCH] alpha: Define pgprot_modify to silence tautological comparison warnings

[PATCH] alpha: Define pgprot_modify to silence tautological comparison warnings

[Matt Turner]

Alpha's pgprot_noncached, pgprot_writecombine, and pgprot_device are
all identity macros, so the generic pgprot_modify() produces
tautological self-comparisons that GCC warns about:

  include/linux/pgtable.h:1701:25: warning: self-comparison always
  evaluates to true [-Wtautological-compare]

Since all caching attributes are no-ops on Alpha, define
pgprot_modify() to simply return newprot.

Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Matt Turner <mattst88@gmail.com>
---
 arch/alpha/include/asm/pgtable.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git ./arch/alpha/include/asm/pgtable.h ./arch/alpha/include/asm/pgtable.h
index e786f630de5c..849abe2a1f98 100644
--- ./arch/alpha/include/asm/pgtable.h
+++ ./arch/alpha/include/asm/pgtable.h
@@ -126,6 +126,17 @@ struct vm_area_struct;
  */
 #define pgprot_noncached(prot)	(prot)
 
+/*
+ * All caching attribute macros are identity on Alpha, so the generic
+ * pgprot_modify() degenerates to tautological self-comparisons.
+ * Override it to just return newprot directly.
+ */
+#define pgprot_modify pgprot_modify
+static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
+{
+	return newprot;
+}
+
 /*
  * ZERO_PAGE is a global shared page that is always zero:  used
  * for zero-mapped memory areas etc..
-- 
2.52.0

Re: [PATCH] alpha: Define pgprot_modify to silence tautological comparison warnings

[Magnus Lindholm]

On Fri, Apr 3, 2026 at 5:01 PM Matt Turner <mattst88@gmail.com> wrote:
>
> Alpha's pgprot_noncached, pgprot_writecombine, and pgprot_device are
> all identity macros, so the generic pgprot_modify() produces
> tautological self-comparisons that GCC warns about:
>
>   include/linux/pgtable.h:1701:25: warning: self-comparison always
>   evaluates to true [-Wtautological-compare]
>
> Since all caching attributes are no-ops on Alpha, define
> pgprot_modify() to simply return newprot.
>
> Assisted-by: Claude:claude-opus-4-6
> Signed-off-by: Matt Turner <mattst88@gmail.com>
> ---
>  arch/alpha/include/asm/pgtable.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git ./arch/alpha/include/asm/pgtable.h ./arch/alpha/include/asm/pgtable.h
> index e786f630de5c..849abe2a1f98 100644
> --- ./arch/alpha/include/asm/pgtable.h
> +++ ./arch/alpha/include/asm/pgtable.h
> @@ -126,6 +126,17 @@ struct vm_area_struct;
>   */
>  #define pgprot_noncached(prot) (prot)
>
> +/*
> + * All caching attribute macros are identity on Alpha, so the generic
> + * pgprot_modify() degenerates to tautological self-comparisons.
> + * Override it to just return newprot directly.
> + */
> +#define pgprot_modify pgprot_modify
> +static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
> +{
> +       return newprot;
> +}
> +
>  /*
>   * ZERO_PAGE is a global shared page that is always zero:  used
>   * for zero-mapped memory areas etc..
> --

Looks good to me.

Reviewed-by: Magnus Lindholm <linmag7@gmail.com>