linux-kernel - Re: [PATCH 4/4] clk: Warn if we register a mux without determine

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20221026020800.38AC8C433C1@smtp.kernel.org>
Date:   Tue, 25 Oct 2022 19:07:58 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Maxime Ripard <maxime@...no.tech>,
        Michael Turquette <mturquette@...libre.com>
Cc:     linux-kernel@...r.kernel.org,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Maxime Ripard <maxime@...no.tech>, linux-clk@...r.kernel.org
Subject: Re: [PATCH 4/4] clk: Warn if we register a mux without determine_rate

Quoting Maxime Ripard (2022-10-18 06:52:59)
> The determine_rate hook allows to select the proper parent and its rate
> for a given clock configuration. On another hand, set_parent is there to
> change the parent of a mux.
> 
> Some clocks provide a set_parent hook but don't implement
> determine_rate. In such a case, set_parent is pretty much useless since
> the clock framework will always assume the current parent is to be used,
> and we will thus never change it.
> 
> This situation can be solved in two ways:
>   - either we don't need to change the parent, and we thus shouldn't
>     implement set_parent;
>   - or we don't want to change the parent, in this case we should set
>     CLK_SET_RATE_NO_REPARENT;
>   - or we're missing a determine_rate implementation.
> 
> The latter is probably just an oversight from the driver's author, and
> we should thus raise their awareness about the fact that the current
> state of the driver is confusing.

There is another case which is a leaf clk that is a mux where you only
expect clk_set_parent() to be used, and not clk_set_rate(). This use
case is odd though, so I'm not sure how much we care.

> 
> It's not clear at this point how many drivers are affected though, so
> let's make it a warning instead of an error for now.
> 
> Signed-off-by: Maxime Ripard <maxime@...no.tech>
> ---
>  drivers/clk/clk.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 57b83665e5c3..11c41d987ff4 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -3700,6 +3700,11 @@ static int __clk_core_init(struct clk_core *core)
>                 goto out;
>         }
>  
> +       /* TODO: Promote to an error */

The documentation should be updated in this patch (see the table of
hardware characteristics in Documentation/driver-api/clk.rst).

> +       if (core->ops->set_parent && !core->ops->determine_rate)
> +               pr_warn("%s: %s must implement .set_parent & .determine_rate\n",

You can grep for it:

 $ git grep -W 'struct clk_ops .*='

but I'm fairly certain a coccinelle script can detect most of these
because clk_ops are usually statically defined (although not always).

Either way I already see that 'owl_comp_div_ops' will trigger this
warning. And 'at91sam9x5_smd_ops' looks even more likely. Given that I'm
not super keen on applying this patch.