linux-kernel - Re: [Patch v1 01/10] memory: tegra: add interconnect support for DRAM scaling in Tegra234

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Date:   Fri, 13 Jan 2023 17:45:44 +0530
From:   Sumit Gupta <sumitg@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>, <treding@...dia.com>,
        <krzysztof.kozlowski@...aro.org>, <dmitry.osipenko@...labora.com>,
        <viresh.kumar@...aro.org>, <rafael@...nel.org>,
        <jonathanh@...dia.com>, <robh+dt@...nel.org>,
        <linux-kernel@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-pm@...r.kernel.org>, <devicetree@...r.kernel.org>
CC:     Sanjay Chandrashekara <sanjayc@...dia.com>,
        Krishna Sitaraman <ksitaraman@...dia.com>,
        Ishan Shah <ishah@...dia.com>, Bibek Basu <bbasu@...dia.com>,
        Sumit Gupta <sumitg@...dia.com>
Subject: Re: [Patch v1 01/10] memory: tegra: add interconnect support for DRAM
 scaling in Tegra234



On 21/12/22 22:13, Dmitry Osipenko wrote:
> External email: Use caution opening links or attachments
> 
> 
> 21.12.2022 12:35, Sumit Gupta пишет:
>>
>>
>> On 20/12/22 23:40, Dmitry Osipenko wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> 20.12.2022 19:02, Sumit Gupta пишет:
>>>> +static int tegra_emc_icc_get_init_bw(struct icc_node *node, u32
>>>> *avg, u32 *peak)
>>>> +{
>>>> +     *avg = 0;
>>>> +     *peak = 0;
>>>> +
>>>> +     return 0;
>>>> +}
>>>
>>> Looks wrong, you should add ICC support to all the drivers first and
>>> only then enable ICC. I think you added this init_bw() to work around
>>> the fact that ICC isn't supported by T234 drivers.
>>
>> If get_bw hook is not added then max freq is set due to 'INT_MAX' below.
>>
>>   void icc_node_add(struct icc_node *node, struct icc_provider *provider)
>>   {
>>     ....
>>     /* get the initial bandwidth values and sync them with hardware */
>>     if (provider->get_bw) {
>>           provider->get_bw(node, &node->init_avg, &node->init_peak);
>>     } else {
>>           node->init_avg = INT_MAX;
>>           node->init_peak = INT_MAX;
>>   }
>>
>> So, will have to add the empty functions at least.
>>
>>   static int tegra_emc_icc_get_init_bw(struct icc_node *node, u32 *avg,
>> u32 *peak)
>>   {
>> -       *avg = 0;
>> -       *peak = 0;
>> -
>>          return 0;
>>   }
>>
>> Support to all the client drivers can't be added at once as there are
>> many drivers all with different requirements and handling. This patch
>> series is the beginning to add the basic interconnect support in new
>> Tegra SoC's. Support for more clients will be added later one by one or
>> in batch.
> 
> This means that bandwidth management isn't working properly. You should
> leave the freq to INT_MAX and fix the missing integer overflows in the
> code if any, or read out the BW from FW.
> 
> Once you'll enable ICC for all drivers, it will start working.
> 

Referred the below patches and now understand what you mean.
 
https://patchwork.kernel.org/project/linux-arm-msm/cover/20200825170152.6434-1-georgi.djakov@linaro.org/
  https://lore.kernel.org/all/20210912183009.6400-1-digetx@gmail.com/

There is no MRQ currently in BPMP-FW to get the bandwidth for a client.
So, can't add that in get_bw(). As explained earlier, we are in process 
adding of adding support for all clients but that may take some time. We 
can remove the get_bw() calls initializing "*bw = 0" once we have the 
support added in all clients. Noticed that below drivers also do same.

  $ grep -rB3 "*peak = 0" drivers/interconnect/*
  drivers/interconnect/imx/imx.c-static int imx_icc_get_bw(struct 
icc_node *node, u32 *avg, u32 *peak)
  drivers/interconnect/imx/imx.c-{
  drivers/interconnect/imx/imx.c- *avg = 0;
  drivers/interconnect/imx/imx.c: *peak = 0;
  --
  drivers/interconnect/qcom/msm8974.c-static int msm8974_get_bw(struct 
icc_node *node, u32 *avg, u32 *peak)
  drivers/interconnect/qcom/msm8974.c-{
  drivers/interconnect/qcom/msm8974.c-    *avg = 0;
  drivers/interconnect/qcom/msm8974.c:    *peak = 0;