Re: [PATCH v3 0/4] Add Tegra238 BPMP support and fix stale EMC clock rate

[Mikko Perttunen <mperttunen@nvidia.com>]

On Monday, November 2, 2026 9:11 PM Johnny Liu wrote:
> EMC clock scaling is handled by the BPMP firmware without kernel
> involvement, so clk_get_rate() on the EMC clock can return a stale value
> cached by the common clock framework. This series makes the EMC clock
> rate uncached on Tegra234, Tegra238 and Tegra264, and adds the pieces
> needed to identify the EMC clock on each of these chips.
> 
> The EMC clock ID differs per chip (TEGRA234_CLK_EMC=31,
> TEGRA238_CLK_EMC=43, TEGRA264_CLK_EMC=290), while the
> "nvidia,tegra186-bpmp" fallback compatible and the tegra186_soc data are
> shared across several chips. To avoid detecting the chip at runtime, the
> EMC clock ID is carried in per-SoC BPMP data selected by the device tree
> compatible.
> 
> Patch 1 adds the "nvidia,tegra238-bpmp" compatible to the binding,
> together with the Tegra238 clock ID header. Patch 2 adds an emc_clk_id
> field to struct tegra_bpmp_soc, together with dedicated SoC data for
> Tegra234 and Tegra264 built on a common TEGRA186_BPMP_SOC_COMMON
> initializer. Patch 3 adds Tegra238 support to the BPMP driver, including
> its own SoC data and EMC clock ID. Patch 4 then sets
> CLK_GET_RATE_NOCACHE on the clock matching that ID, so that the common
> clock framework forwards rate queries to the BPMP instead of returning a
> stale cached rate.
> 
> The series touches both the clock and the firmware code. Patch 4 depends
> on patch 2, and patch 3 depends on patches 1 and 2, so I would suggest
> taking the whole series through the Tegra tree with an Acked-by from the
> clock maintainers.
> 
> Changes in v3:
> - Move the TEGRA186_BPMP_SOC_COMMON refactoring out of the Tegra238
>   support patch and into the "Add per-SoC EMC clock ID" patch, as the
>   refactoring only makes sense together with the per-SoC emc_clk_id.
> - Keep all Tegra238 specific changes (Makefile, CONFIG_ARCH_TEGRA_238_SOC
>   guards, clock ID header include, tegra238_soc data and compatible match)
>   in a single "Add Tegra238 support" patch, and reorder it after the
>   per-SoC EMC clock ID patch.
> - Reword the "Add per-SoC EMC clock ID" commit message to describe the
>   intended use of emc_clk_id: the BPMP clock provider sets
>   CLK_GET_RATE_NOCACHE on that clock, as it is completely managed by the
>   firmware and the common clock framework must pass rate queries through
>   to get the latest rate.
> - No changes to patches 1 and 4 apart from the patch numbering.
> 
> Changes in v2:
> - Squash "dt-bindings: clock: Add Tegra238 BPMP clock IDs" into
>   "dt-bindings: firmware: tegra186-bpmp: Add Tegra238 compatible".
> - Reword the binding commit message to state that the Tegra238 SoC is
>   fully compatible with the Tegra186 BPMP.
> 
> v2: https://lore.kernel.org/all/20261028155000.1205739-1-johnliu@nvidia.com/
> v1: https://lore.kernel.org/all/20261028084900.1047287-1-johnliu@nvidia.com/
> 
> Johnny Liu (4):
>   dt-bindings: firmware: tegra186-bpmp: Add Tegra238 BPMP
>   firmware: tegra: bpmp: Add per-SoC EMC clock ID
>   firmware: tegra: bpmp: Add Tegra238 support
>   clk: tegra: bpmp: Do not cache the EMC clock rate
> 
>  .../firmware/nvidia,tegra186-bpmp.yaml        |   1 +
>  drivers/clk/tegra/clk-bpmp.c                  |   3 +
>  drivers/firmware/tegra/Makefile               |   1 +
>  drivers/firmware/tegra/bpmp.c                 |  61 ++--
>  include/dt-bindings/clock/nvidia,tegra238.h   | 279 ++++++++++++++++++
>  include/soc/tegra/bpmp.h                      |   1 +
>  6 files changed, 329 insertions(+), 17 deletions(-)
>  create mode 100644 include/dt-bindings/clock/nvidia,tegra238.h
> 
> -- 
> 2.43.0
> 
> 

Thank you!

Reviewed-by: Mikko Perttunen <mperttunen@nvidia.com>