linux-kernel - Re: [PATCH net v3 3/3] rtase: Fix a type error in min

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Message-ID: <20250423161608.GB2843373@horms.kernel.org>
Date: Wed, 23 Apr 2025 17:16:08 +0100
From: Simon Horman <horms@...nel.org>
To: Justin Lai <justinlai0215@...ltek.com>
Cc: "kuba@...nel.org" <kuba@...nel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"pabeni@...hat.com" <pabeni@...hat.com>,
	"andrew+netdev@...n.ch" <andrew+netdev@...n.ch>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Ping-Ke Shih <pkshih@...ltek.com>,
	Larry Chiu <larry.chiu@...ltek.com>, Andrew Lunn <andrew@...n.ch>,
	David Laight <david.laight.linux@...il.com>
Subject: Re: [PATCH net v3 3/3] rtase: Fix a type error in min_t

On Wed, Apr 23, 2025 at 10:53:53AM +0000, Justin Lai wrote:
> > 
> > + David Laight
> > 
> > On Thu, Apr 17, 2025 at 04:56:59PM +0800, Justin Lai wrote:
> > > Fix a type error in min_t.
> > >
> > > Fixes: a36e9f5cfe9e ("rtase: Add support for a pci table in this
> > > module")
> > > Signed-off-by: Justin Lai <justinlai0215@...ltek.com>
> > > Reviewed-by: Andrew Lunn <andrew@...n.ch>
> > > ---
> > >  drivers/net/ethernet/realtek/rtase/rtase_main.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/ethernet/realtek/rtase/rtase_main.c
> > > b/drivers/net/ethernet/realtek/rtase/rtase_main.c
> > > index 55b8d3666153..bc856fb3d6f3 100644
> > > --- a/drivers/net/ethernet/realtek/rtase/rtase_main.c
> > > +++ b/drivers/net/ethernet/realtek/rtase/rtase_main.c
> > > @@ -1923,7 +1923,7 @@ static u16 rtase_calc_time_mitigation(u32
> > time_us)
> > >       u8 msb, time_count, time_unit;
> > >       u16 int_miti;
> > >
> > > -     time_us = min_t(int, time_us, RTASE_MITI_MAX_TIME);
> > > +     time_us = min_t(u32, time_us, RTASE_MITI_MAX_TIME);
> > 
> > Hi Justin, Andrew, David, all,
> > 
> > I may be on the wrong track here, but near the top of minmax.h I see:
> > 
> > /*
> >  * min()/max()/clamp() macros must accomplish several things:
> >  *
> >  * - Avoid multiple evaluations of the arguments (so side-effects like
> >  *   "x++" happen only once) when non-constant.
> >  * - Perform signed v unsigned type-checking (to generate compile
> >  *   errors instead of nasty runtime surprises).
> >  * - Unsigned char/short are always promoted to signed int and can be
> >  *   compared against signed or unsigned arguments.
> >  * - Unsigned arguments can be compared against non-negative signed
> > constants.
> >  * - Comparison of a signed argument against an unsigned constant fails
> >  *   even if the constant is below __INT_MAX__ and could be cast to int.
> >  */
> > 
> > So, considering the 2nd last point, I think we can simply use min() both above
> > and below. Which would avoid the possibility of casting to the wrong type again
> > in future.
> > 
> > Also, aside from which call is correct. Please add some colour to the commit
> > message describing why this is a bug if it is to be treated as a fix for net rather
> > than a clean-up for net-next.
> > 
> > >
> > >       if (time_us > RTASE_MITI_TIME_COUNT_MASK) {
> > >               msb = fls(time_us);
> > > @@ -1945,7 +1945,7 @@ static u16 rtase_calc_packet_num_mitigation(u16
> > pkt_num)
> > >       u8 msb, pkt_num_count, pkt_num_unit;
> > >       u16 int_miti;
> > >
> > > -     pkt_num = min_t(int, pkt_num, RTASE_MITI_MAX_PKT_NUM);
> > > +     pkt_num = min_t(u16, pkt_num, RTASE_MITI_MAX_PKT_NUM);
> > >
> > >       if (pkt_num > 60) {
> > >               pkt_num_unit = RTASE_MITI_MAX_PKT_NUM_IDX;
> > > --
> > > 2.34.1
> > >
> 
> Hi Simon,
> 
> According to a more detailed clarification, this part is actually an
> enhancement and does not cause any issues during operation, so it is
> not a real bug. Therefore, I will post this patch in net-next.

Thanks. Please do consider using min() instead of min_t() when you post the
patch to net-next.