netdev - Re: [PATCH net-next] net: mvpp2: Improve data types and use min()

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Message-ID: <20240715183922.GA263242@kernel.org>
Date: Mon, 15 Jul 2024 19:39:22 +0100
From: Simon Horman <horms@...nel.org>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Thorsten Blum <thorsten.blum@...lux.com>, marcin.s.wojtas@...il.com,
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: mvpp2: Improve data types and use min()

On Mon, Jul 15, 2024 at 04:44:01PM +0100, Russell King (Oracle) wrote:
> On Thu, Jul 11, 2024 at 05:47:43PM +0200, Thorsten Blum wrote:
> > Change the data type of the variable freq in mvpp2_rx_time_coal_set()
> > and mvpp2_tx_time_coal_set() to u32 because port->priv->tclk also has
> > the data type u32.
> > 
> > Change the data type of the function parameter clk_hz in
> > mvpp2_usec_to_cycles() and mvpp2_cycles_to_usec() to u32 accordingly
> > and remove the following Coccinelle/coccicheck warning reported by
> > do_div.cocci:
> > 
> >   WARNING: do_div() does a 64-by-32 division, please consider using div64_ul instead
> > 
> > Use min() to simplify the code and improve its readability.
> > 
> > Compile-tested only.
> > 
> > Signed-off-by: Thorsten Blum <thorsten.blum@...lux.com>
> 
> I'm still on holiday, but it's a wet day today. Don't expect replies
> from me to be regular.
> 
> I don't think this is a good idea.
> 
> priv->tclk comes from clk_get_rate() which returns an unsigned long.
> tclk should _also_ be an unsigned long, not a u32, so that the range
> of values clk_get_rate() returns can be represented without being
> truncted.
> 
> Thus the use of unsigned long elsewhere where tclk is passed into is
> actually correct.
> 
> If we need to limit tclk to values that u32 can represent, then that
> needs to be done here:
> 
>                 priv->tclk = clk_get_rate(priv->pp_clk);
> 
> by assigning the return value to an unsigned long local variable,
> then checking its upper liit before assigning it to priv->tclk.

Sorry, I thought that I had checked the types.
But clearly I wasn't nearly careful enough.