linux-kernel - Re: [PATCH 2/3] firmware: arm_scmi: Fix freq/power truncation in the perf protocol

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Message-ID: <20231130195154.hid7darksc4skxqp@bogus>
Date:   Thu, 30 Nov 2023 19:51:54 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Cristian Marussi <cristian.marussi@....com>
Cc:     Sibi Sankar <quic_sibis@...cinc.com>,
        linux-arm-msm@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>,
        linux-kernel@...r.kernel.org, quic_mdtipton@...cinc.com,
        linux-arm-kernel@...ts.infradead.org, quic_asartor@...cinc.com,
        quic_lingutla@...cinc.com
Subject: Re: [PATCH 2/3] firmware: arm_scmi: Fix freq/power truncation in the
 perf protocol

On Thu, Nov 30, 2023 at 04:25:44PM +0000, Cristian Marussi wrote:
> On Thu, Nov 30, 2023 at 01:56:56PM +0000, Sudeep Holla wrote:
> > I started exactly with that, but when I completed the patch, there was no
> > explicit need for it, so dropped it again. I can bump mult_factor to be
> > u64 but do you see any other place that would need it apart from having
> > single statement that does multiplication and assignment ? I am exploiting
> > the conditional based on level_indexing_mode here but I agree it may help
> > in backporting if I make mult_factor u64.
> > 
> 
> Ah right
> 
>    freq *= dom->multi_fact;
> 
> does the trick..but cannot this by itself (under unplausibl conds)
> overflow and does not fit into a u32 mult_factor ?
> 
>  dom_info->mult_factor =
>  	(dom_info->sustained_freq_khz * 1000UL)
> 	/ dom_info->sustained_perf_level;

Agreed. Also thinking about backports, I think making it u64 is simple
fix. I will also thinking of splitting the changes so that fixes are
more appropriate. I will try to post something soonish.

--
Regards,
Sudeep