Re: [Patch v7 1/8] memory: tegra: add interconnect support for DRAM scaling in Tegra234

[Sumit Gupta <sumitg@nvidia.com>]

On 24/04/23 19:18, Krzysztof Kozlowski wrote:
> External email: Use caution opening links or attachments
> 
> 
> On 24/04/2023 15:13, Sumit Gupta wrote:
>> Add Interconnect framework support to dynamically set the DRAM
>> bandwidth from different clients. Both the MC and EMC drivers are
>> added as ICC providers. The path for any request is:
>>   MC-Client[1-n] -> MC -> EMC -> EMEM/DRAM
>>
> Thank you for your patch. There is something to discuss/improve.
> 
> 
>> +static int tegra_emc_interconnect_init(struct tegra186_emc *emc)
>> +{
>> +     struct tegra_mc *mc = dev_get_drvdata(emc->dev->parent);
>> +     const struct tegra_mc_soc *soc = mc->soc;
>> +     struct icc_node *node;
>> +     int err;
>> +
>> +     emc->provider.dev = emc->dev;
>> +     emc->provider.set = tegra_emc_icc_set_bw;
>> +     emc->provider.data = &emc->provider;
>> +     emc->provider.aggregate = soc->icc_ops->aggregate;
>> +     emc->provider.xlate = tegra_emc_of_icc_xlate;
>> +     emc->provider.get_bw = tegra_emc_icc_get_init_bw;
>> +
>> +     icc_provider_init(&emc->provider);
>> +
>> +     /* create External Memory Controller node */
>> +     node = icc_node_create(TEGRA_ICC_EMC);
>> +     if (IS_ERR(node)) {
>> +             err = PTR_ERR(node);
>> +             goto err_msg;
>> +     }
>> +
>> +     node->name = "External Memory Controller";
>> +     icc_node_add(node, &emc->provider);
>> +
>> +     /* link External Memory Controller to External Memory (DRAM) */
>> +     err = icc_link_create(node, TEGRA_ICC_EMEM);
>> +     if (err)
>> +             goto remove_nodes;
>> +
>> +     /* create External Memory node */
>> +     node = icc_node_create(TEGRA_ICC_EMEM);
>> +     if (IS_ERR(node)) {
>> +             err = PTR_ERR(node);
>> +             goto remove_nodes;
>> +     }
>> +
>> +     node->name = "External Memory (DRAM)";
>> +     icc_node_add(node, &emc->provider);
>> +
>> +     err = icc_provider_register(&emc->provider);
>> +     if (err)
>> +             goto remove_nodes;
>> +
>> +     return 0;
>> +
>> +remove_nodes:
>> +     icc_nodes_remove(&emc->provider);
>> +err_msg:
>> +     dev_err(emc->dev, "failed to initialize ICC: %d\n", err);
>> +
>> +     return err;
>> +}
>> +
>>   static int tegra186_emc_probe(struct platform_device *pdev)
>>   {
>> +     struct tegra_mc *mc = dev_get_drvdata(pdev->dev.parent);
>>        struct mrq_emc_dvfs_latency_response response;
>>        struct tegra_bpmp_message msg;
>>        struct tegra186_emc *emc;
>> @@ -236,6 +339,29 @@ static int tegra186_emc_probe(struct platform_device *pdev)
>>        debugfs_create_file("max_rate", S_IRUGO | S_IWUSR, emc->debugfs.root,
>>                            emc, &tegra186_emc_debug_max_rate_fops);
>>
>> +     if (mc && mc->soc->icc_ops) {
>> +             /*
>> +              * Initialize the ICC even if BPMP-FW doesn't support 'MRQ_BWMGR_INT'.
>> +              * Use the flag 'mc->bwmgr_mrq_supported' within MC driver and return
>> +              * EINVAL instead of passing the request to BPMP-FW later when the BW
>> +              * request is made by client with 'icc_set_bw()' call.
>> +              */
>> +             err = tegra_emc_interconnect_init(emc);
>> +             if (err)
>> +                     goto put_bpmp;
>> +
>> +             if (tegra_bpmp_mrq_is_supported(emc->bpmp, MRQ_BWMGR_INT)) {
>> +                     mc->bwmgr_mrq_supported = true;
>> +
>> +                     /*
>> +                      * MC driver probe can't get BPMP reference as it gets probed
>> +                      * earlier than BPMP. So, save the BPMP ref got from the EMC
>> +                      * DT node in the mc->bpmp and use it in MC's icc_set hook.
>> +                      */
>> +                     mc->bpmp = emc->bpmp;
> 
> This (and ()) are called without any locking. You register first the
> interconnect, so set() callback can be used, right? Then set() could be
> called anytime between tegra_emc_interconnect_init() and assignment
> above. How do you synchronize these?
> 
> Best regards,
> Krzysztof
> 

Currently, the tegra234_mc_icc_set() has NULL check. So, it will give 
this error.
  if (!mc->bpmp) {
          dev_err(mc->dev, "BPMP reference NULL\n");
          return -ENOENT;
  }

To fix, we can do the below change and swap the order. Please let me 
know if this sounds fine ?
  if (mc && mc->soc->icc_ops) {
          if (tegra_bpmp_mrq_is_supported(emc->bpmp, MRQ_BWMGR_INT)) {
                  mc->bwmgr_mrq_supported = true;
                  mc->bpmp = emc->bpmp;
          }

          err = tegra_emc_interconnect_init(emc);
          if (err)
                  goto put_bpmp;

  }

Thank you,
Sumit Gupta