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

Krzysztof Kozlowski
2023-04-24T13:49:07Z

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