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

Aaron Kling
2025-11-10T21:55:32Z

On Mon, Nov 10, 2025 at 3:25 PM Jon Hunter <jonathanh@nvidia.com> wrote:
>
>
> 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.

Interesting. Both were booting for me during my verification, though
my use case involves the dt changes that I don't believe have been
picked up yet. Thought I had explicitly verified without the dt
changes too, though. Since I was asked to do so on this or one of the
other similar series. I will try to check linux-next as-is soon.

Aaron