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

Aaron Kling
2025-11-11T01:39:18Z

On Mon, Nov 10, 2025 at 3:55 PM Aaron Kling <webgeek1234@gmail.com> wrote:
>
> 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.

I just built next-20251110 using the standard arm64 defconfig and
flashed the resulting Image and dtb's to p2972 and p3518 (p3509+p3668)
and both booted to cli on a barebones busybox ramdisk. I do not see
any errors from tegra-mc, and the only error I see from tegra186-emc
is that it can't find the opp tables, which is expected without the dt
changes, and is not fatal.

Aaron