linux-kernel - Re: [PATCH] tty: gdm724x: use min_t() for size

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Message-ID: <e76ddc3-4843-a6bb-6b32-92dc5ca3e178@linux-m68k.org>
Date:   Wed, 16 Aug 2023 13:45:13 +0200 (CEST)
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Jiri Slaby (SUSE)" <jirislaby@...nel.org>
cc:     gregkh@...uxfoundation.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] tty: gdm724x: use min_t() for size_t varable and a
 constant

On Wed, 16 Aug 2023, Jiri Slaby (SUSE) wrote:
> My thinking was that ulong is the same as size_t everywhere. No, size_t
> is uint on 32bit. So the below commit introduced a build warning on
> 32bit:
> .../gdm724x/gdm_tty.c:165:24: warning: comparison of distinct pointer types ('typeof (2048UL) *' (aka 'unsigned long *') and 'typeof (remain) *' (aka 'unsigned int *'))
>
> To fix this, partially revert the commit (remove constants' suffixes)
> and switch to min_t() in this case instead.
>
> /me would hope for Z (or alike) suffix for constants.
>
> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@...nel.org>
> Fixes: c3e5c706aefc (tty: gdm724x: convert counts to size_t)
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202308151953.rNNnAR2N-lkp@intel.com/

Thanks, this fixes the m68k/allmodconfig build.

Reviewed-by: Geert Uytterhoeven <geert@...ux-m68k.org>

> --- a/drivers/staging/gdm724x/gdm_tty.c
> +++ b/drivers/staging/gdm724x/gdm_tty.c
> @@ -17,9 +17,9 @@
> #define GDM_TTY_MAJOR 0
> #define GDM_TTY_MINOR 32
>
> -#define WRITE_SIZE 2048UL
> +#define WRITE_SIZE 2048
>
> -#define MUX_TX_MAX_SIZE 2048UL
> +#define MUX_TX_MAX_SIZE 2048

You probably want to keep the "U" suffix, so at least both parts
of min() are unsigned.

See also "[PATCH next v3 0/5] minmax: Relax type checks in min() and max().".
https://lore.kernel.org/all/01e3e09005e9434b8f558a893a47c053@AcuMS.aculab.com,

>
> static inline bool gdm_tty_ready(struct gdm *gdm)
> {
> @@ -159,7 +159,7 @@ static ssize_t gdm_tty_write(struct tty_struct *tty, const u8 *buf, size_t len)
> 		return -ENODEV;
>
> 	while (remain) {
> -		size_t sending_len = min(MUX_TX_MAX_SIZE, remain);
> +		size_t sending_len = min_t(size_t, MUX_TX_MAX_SIZE, remain);
> 		gdm->tty_dev->send_func(gdm->tty_dev->priv_dev,
> 					(void *)(buf + sent_len),
> 					sending_len,
> -- 
> 2.41.0
>
>

Gr{oetje,eeting}s,

 						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
 							    -- Linus Torvalds