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

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Date:   Thu, 30 Nov 2023 13:56:56 +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, 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 12:49:42PM +0000, Cristian Marussi wrote:
> On Thu, Nov 30, 2023 at 12:05:06PM +0000, Sudeep Holla wrote:
> > On Wed, Nov 29, 2023 at 12:27:47PM +0530, Sibi Sankar wrote:
> > > Fix frequency and power truncation seen in the performance protocol by
> > > casting it with the correct type.
> > >
> > 
> > While I always remembered to handle this when reviewing the spec, seem to
> > have forgotten when it came to handling in the implementation :(. Thanks
> > for spotting this.
> > 
> > However I don't like the ugly type casting. I think we can do better. Also
> > looking at the code around the recently added level index mode, I think we
> > can simplify things like below patch.
> > 
> > Cristian,
> > What do you think ?
> > 
> 
> Hi
> 
> the cleanup seems nice in general to compact the mult_factor multipliers
> in one place, and regarding addressing the problem of truncation without
> the need of the explicit casting, should not be enough to change to
> additionally also change mult_factor to be an u64 ?
>

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.

-- 
Regards,
Sudeep