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

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Message-ID: <e082032238ae4d5e9af2c0ccdc79889f@AcuMS.aculab.com>
Date:   Thu, 17 Aug 2023 11:37:25 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Jiri Slaby (SUSE)'" <jirislaby@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...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

From: Jiri Slaby (SUSE)
> Sent: Wednesday, August 16, 2023 9:53 AM
> 
> 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.
> 
....
> -		size_t sending_len = min(MUX_TX_MAX_SIZE, remain);
> +		size_t sending_len = min_t(size_t, MUX_TX_MAX_SIZE, remain);

It would be slightly safer to use:
		min(remain, (size_t)MAX_TX_MAX_SIZE);
since that maintains the type check.
(It is also nicer to put the constant second.)

	David

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