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

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Date:   Wed, 21 Dec 2022 19:43:44 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sumit Gupta <sumitg@...dia.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
Subject: Re: [Patch v1 01/10] memory: tegra: add interconnect support for DRAM
 scaling in Tegra234

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.