linux-kernel - Re: [PATCH v2 03/10] interconnect: qcom: icc-rpm: Let nodes drive their own bus clock

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Message-ID: <ZMjlZyFcB9IFEG60@gerhold.net>
Date:   Tue, 1 Aug 2023 12:58:47 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Georgi Djakov <djakov@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH v2 03/10] interconnect: qcom: icc-rpm: Let nodes drive
 their own bus clock

On Mon, Jul 31, 2023 at 12:52:19PM +0200, Konrad Dybcio wrote:
> If this hardware couldn't get messier, some nodes are supposed to drive
> their own bus clock.. Presumably to connect to some intermediate
> interface between the node itself and the bus it's (supposed to be)
> connected to.
> 
> Expand the node struct with the necessary data and hook up the
> allocations & calculations.
> 
> To save on memory (not very many nodes have their own clocks), allocate
> a pointer to an array instead of allocating an array within
> qcom_icc_node.
> 

Only on ARM32 though. On ARM64 you waste extra memory:

u32 bus_clk_rate[QCOM_SMD_RPM_STATE_NUM];
sizeof(bus_clk_rate) = QCOM_SMD_RPM_STATE_NUM * sizeof(bus_clk_rate[0])
                     = 2 * 4
                     = 8

u32 *bus_clk_rate;
sizeof(bus_clk_rate) = sizeof(ptr)
                     = 8 (for ARM64)
                       + 2 * 4 + malloc overhead
                         for each node with bus_clk_desc

which is > 8 from above.

I'm not quite convinced this optimization is worth it.

Thanks,
Stephan