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

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Date:   Tue, 1 Aug 2023 13:29:16 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Stephan Gerhold <stephan@...hold.net>
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 1.08.2023 12:58, Stephan Gerhold wrote:
> 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.
Right, u32 is not the same size as *u32, brain fart :D

Konrad