Re: [PATCH v4 3/5] memory: tegra186-emc: Support non-bpmp icc scaling

Jon Hunter
2025-11-10T21:25:21Z

On 27/10/2025 18:55, Aaron Kling via B4 Relay wrote:
> From: Aaron Kling <webgeek1234@gmail.com>
>
> This adds support for dynamic frequency scaling of external memory on
> devices with bpmp firmware that does not support bwmgr.
>
> Signed-off-by: Aaron Kling <webgeek1234@gmail.com>
> ---
> drivers/memory/tegra/tegra186-emc.c | 132 +++++++++++++++++++++++++++++++++++-
> 1 file changed, 130 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/memory/tegra/tegra186-emc.c b/drivers/memory/tegra/tegra186-emc.c
> index 9959ad5804b444b269456d1fbae87b4bc111661b..74be09968baa7a0fbdce4359f470ce56b18acb10 100644
> --- a/drivers/memory/tegra/tegra186-emc.c
> +++ b/drivers/memory/tegra/tegra186-emc.c
> @@ -18,6 +18,17 @@ struct tegra186_emc_dvfs {
> unsigned long rate;
> };
>
> +enum emc_rate_request_type {
> + EMC_RATE_DEBUG,
> + EMC_RATE_ICC,
> + EMC_RATE_TYPE_MAX,
> +};
> +
> +struct emc_rate_request {
> + unsigned long min_rate;
> + unsigned long max_rate;
> +};
> +
> struct tegra186_emc {
> struct tegra_bpmp *bpmp;
> struct device *dev;
> @@ -33,8 +44,90 @@ struct tegra186_emc {
> } debugfs;
>
> struct icc_provider provider;
> +
> + /*
> + * There are multiple sources in the EMC driver which could request
> + * a min/max clock rate, these rates are contained in this array.
> + */
> + struct emc_rate_request requested_rate[EMC_RATE_TYPE_MAX];
> +
> + /* protect shared rate-change code path */
> + struct mutex rate_lock;
> };
>
> +static void tegra186_emc_rate_requests_init(struct tegra186_emc *emc)
> +{
> + unsigned int i;
> +
> + for (i = 0; i < EMC_RATE_TYPE_MAX; i++) {
> + emc->requested_rate[i].min_rate = 0;
> + emc->requested_rate[i].max_rate = ULONG_MAX;
> + }
> +}
> +
> +static int emc_request_rate(struct tegra186_emc *emc,
> + unsigned long new_min_rate,
> + unsigned long new_max_rate,
> + enum emc_rate_request_type type)
> +{
> + struct emc_rate_request *req = emc->requested_rate;
> + unsigned long min_rate = 0, max_rate = ULONG_MAX;
> + unsigned int i;
> + int err;
> +
> + /* select minimum and maximum rates among the requested rates */
> + for (i = 0; i < EMC_RATE_TYPE_MAX; i++, req++) {
> + if (i == type) {
> + min_rate = max(new_min_rate, min_rate);
> + max_rate = min(new_max_rate, max_rate);
> + } else {
> + min_rate = max(req->min_rate, min_rate);
> + max_rate = min(req->max_rate, max_rate);
> + }
> + }
> +
> + if (min_rate > max_rate) {
> + dev_err_ratelimited(emc->dev, "%s: type %u: out of range: %lu %lu\n",
> + __func__, type, min_rate, max_rate);
> + return -ERANGE;
> + }
> +
> + err = clk_set_rate(emc->clk, min_rate);
> + if (err)
> + return err;
> +
> + emc->requested_rate[type].min_rate = new_min_rate;
> + emc->requested_rate[type].max_rate = new_max_rate;
> +
> + return 0;
> +}
> +
> +static int emc_set_min_rate(struct tegra186_emc *emc, unsigned long rate,
> + enum emc_rate_request_type type)
> +{
> + struct emc_rate_request *req = &emc->requested_rate[type];
> + int ret;
> +
> + mutex_lock(&emc->rate_lock);
> + ret = emc_request_rate(emc, rate, req->max_rate, type);
> + mutex_unlock(&emc->rate_lock);
> +
> + return ret;
> +}
> +
> +static int emc_set_max_rate(struct tegra186_emc *emc, unsigned long rate,
> + enum emc_rate_request_type type)
> +{
> + struct emc_rate_request *req = &emc->requested_rate[type];
> + int ret;
> +
> + mutex_lock(&emc->rate_lock);
> + ret = emc_request_rate(emc, req->min_rate, rate, type);
> + mutex_unlock(&emc->rate_lock);
> +
> + return ret;
> +}
> +
> /*
> * debugfs interface
> *
> @@ -107,7 +200,7 @@ static int tegra186_emc_debug_min_rate_set(void *data, u64 rate)
> if (!tegra186_emc_validate_rate(emc, rate))
> return -EINVAL;
>
> - err = clk_set_min_rate(emc->clk, rate);
> + err = emc_set_min_rate(emc, rate, EMC_RATE_DEBUG);
> if (err < 0)
> return err;
>
> @@ -137,7 +230,7 @@ static int tegra186_emc_debug_max_rate_set(void *data, u64 rate)
> if (!tegra186_emc_validate_rate(emc, rate))
> return -EINVAL;
>
> - err = clk_set_max_rate(emc->clk, rate);
> + err = emc_set_max_rate(emc, rate, EMC_RATE_DEBUG);
> if (err < 0)
> return err;
>
> @@ -217,6 +310,12 @@ static int tegra186_emc_get_emc_dvfs_latency(struct tegra186_emc *emc)
> return 0;
> }
>
> +static inline struct tegra186_emc *
> +to_tegra186_emc_provider(struct icc_provider *provider)
> +{
> + return container_of(provider, struct tegra186_emc, provider);
> +}
> +
> /*
> * tegra186_emc_icc_set_bw() - Set BW api for EMC provider
> * @src: ICC node for External Memory Controller (EMC)
> @@ -227,6 +326,33 @@ static int tegra186_emc_get_emc_dvfs_latency(struct tegra186_emc *emc)
> */
> static int tegra186_emc_icc_set_bw(struct icc_node *src, struct icc_node *dst)
> {
> + struct tegra186_emc *emc = to_tegra186_emc_provider(dst->provider);
> + struct tegra_mc *mc = dev_get_drvdata(emc->dev->parent);
> + unsigned long long peak_bw = icc_units_to_bps(dst->peak_bw);
> + unsigned long long avg_bw = icc_units_to_bps(dst->avg_bw);
> + unsigned long long rate = max(avg_bw, peak_bw);
> + const unsigned int ddr = 2;
> + int err;
> +
> + /*
> + * Do nothing here if bwmgr is supported in BPMP-FW. BPMP-FW sets the final
> + * Freq based on the passed values.
> + */
> + if (mc->bwmgr_mrq_supported)
> + return 0;
> +
> + /*
> + * Tegra186 EMC runs on a clock rate of SDRAM bus. This means that
> + * EMC clock rate is twice smaller than the peak data rate because
> + * data is sampled on both EMC clock edges.
> + */
> + do_div(rate, ddr);
> + rate = min_t(u64, rate, U32_MAX);
> +
> + err = emc_set_min_rate(emc, rate, EMC_RATE_ICC);
> + if (err)
> + return err;
> +
> return 0;
> }
>
> @@ -329,6 +455,8 @@ static int tegra186_emc_probe(struct platform_device *pdev)
> platform_set_drvdata(pdev, emc);
> emc->dev = &pdev->dev;
>
> + tegra186_emc_rate_requests_init(emc);
> +
> if (tegra_bpmp_mrq_is_supported(emc->bpmp, MRQ_EMC_DVFS_LATENCY)) {
> err = tegra186_emc_get_emc_dvfs_latency(emc);
> if (err)
>

FYI, this patch is causing a boot regression on Tegra194 devices. I
noticed that tegra194-p2972-0000 and tegra194-p3509-0000+p3668-0000 are
no longer booting and bisect is pointing to this. I will have a closer
look and try to see why this is.

Jon

--
nvpublic