linux-kernel - Re: [PATCH][next] soc: xilinx: vcu: remove deadcode on null divider check

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Message-ID: <161307031421.1254594.40010291545314425@swboyd.mtv.corp.google.com>
Date:   Thu, 11 Feb 2021 11:05:14 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Michael Tretter <m.tretter@...gutronix.de>
Cc:     Colin King <colin.king@...onical.com>,
        Michael Turquette <mturquette@...libre.com>,
        Michal Simek <michal.simek@...inx.com>,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] soc: xilinx: vcu: remove deadcode on null divider check

Quoting Michael Tretter (2021-02-10 23:39:06)
> On Wed, 10 Feb 2021 19:28:18 -0800, Stephen Boyd wrote:
> > Quoting Colin King (2021-02-10 10:49:38)
> > > From: Colin Ian King <colin.king@...onical.com>
> > > 
> > > The pointer 'divider' has previously been null checked followed by
> > > a return, hence the subsequent null check is redundant deadcode
> > > that can be removed.  Clean up the code and remove it.
> > > 
> > > Fixes: 9c789deea206 ("soc: xilinx: vcu: implement clock provider for output clocks")
> > > Signed-off-by: Colin Ian King <colin.king@...onical.com>
> > > ---
> > >  drivers/clk/xilinx/xlnx_vcu.c | 3 ---
> > >  1 file changed, 3 deletions(-)
> > > 
> > > diff --git a/drivers/clk/xilinx/xlnx_vcu.c b/drivers/clk/xilinx/xlnx_vcu.c
> > > index d66b1315114e..607936d7a413 100644
> > > --- a/drivers/clk/xilinx/xlnx_vcu.c
> > > +++ b/drivers/clk/xilinx/xlnx_vcu.c
> > > @@ -512,9 +512,6 @@ static void xvcu_clk_hw_unregister_leaf(struct clk_hw *hw)
> > >  
> > >         mux = clk_hw_get_parent(divider);
> > >         clk_hw_unregister_mux(mux);
> > > -       if (!divider)
> > > -               return;
> > > -
> > 
> > This code is pretty confusing. Waiting for m.tretter@...gutronix.de to
> > reply
> 
> Can you elaborate what you find confusing about this code. I would gladly try
> to clarify and improve the code.

The fact that pointers are being checked and then bailing out of the
function early, vs. doing something if the pointer is non-NULL.

> 
> What happens here is that the driver registers a mux -> divider -> gate chain
> for each output clock, but only stores the gate clock. When unregistering the
> clocks, the driver starts at the gate and walks up to the mux while
> unregistering the clocks.
>