linux-kernel - Re: [PATCH] clk: visconti: Remove dead code

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Date:   Mon, 31 Jan 2022 20:55:46 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>,
        kernel@...labora.com, kernel-janitors@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: visconti: Remove dead code

On Fri, Jan 28, 2022 at 09:35:27PM +0500, Muhammad Usama Anjum wrote:
> rs_id is of unsigned type, u8. The condition rs_id >= 0 will always be
> true. Remove the if-else condition and the dead code.
> 

No, this isn't the right fix.

> Signed-off-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
> ---
>  drivers/clk/visconti/clkc.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/clk/visconti/clkc.c b/drivers/clk/visconti/clkc.c
> index 56a8a4ffebca8..5ccf771d05985 100644
> --- a/drivers/clk/visconti/clkc.c
> +++ b/drivers/clk/visconti/clkc.c
> @@ -147,13 +147,9 @@ int visconti_clk_register_gates(struct visconti_clk_provider *ctx,
>  		if (!dev_name)
>  			return -ENOMEM;
>  
> -		if (clks[i].rs_id >= 0) {
> -			rson_offset = reset[clks[i].rs_id].rson_offset;
> -			rsoff_offset = reset[clks[i].rs_id].rsoff_offset;
> -			rs_idx = reset[clks[i].rs_id].rs_idx;
> -		} else {
> -			rson_offset = rsoff_offset = rs_idx = -1;
> -		}
> +		rson_offset = reset[clks[i].rs_id].rson_offset;
> +		rsoff_offset = reset[clks[i].rs_id].rsoff_offset;
> +		rs_idx = reset[clks[i].rs_id].rs_idx;

With Smatch you can type:

$ smdb.py where visconti_clk_gate_table rs_id
drivers/clk/visconti/clkc-tmpv770x.c | (null)                         | (struct visconti_clk_gate_table)->rs_id | 0-31,255

That tells you it is assigned 255 as a global in drivers/clk/visconti/clkc-tmpv770x.c
It takes some digging to find that assignment...

drivers/clk/visconti/clkc-tmpv770x.c
   175                /* PISYSTEM */
   176                { TMPV770X_CLK_WRCK, "wrck",
   177                        clks_parent_data, ARRAY_SIZE(clks_parent_data),
   178                        0, 0x68, 0x168, 9, 32,
   179                        -1, }, /* No reset */
                              ^^
Really, that -1 there should generate a static checker warning but it
doesn't on Smatch...  :/

But the probably the correct fix is to make rs_id and related variables
and int instead of a u8.  I saw this bug but just reported it instead of
fixing it.

regards,
dan carpenter