On Wed, Feb 19, 2025 at 04:27:39PM -0600, Rob Herring wrote: > On Thu, Feb 13, 2025 at 04:22:17PM +0100, Stephan Gerhold wrote: > > On Thu, Feb 13, 2025 at 03:00:00PM +0100, Konrad Dybcio wrote: > > > On 13.02.2025 10:13 AM, Stephan Gerhold wrote: > > > > On Wed, Feb 12, 2025 at 10:01:59PM +0100, Konrad Dybcio wrote: > > > >> On 12.02.2025 6:03 PM, Stephan Gerhold wrote: > > > >>> num-channels and qcom,num-ees are required when there are no clocks > > > >>> specified in the device tree, because we have no reliable way to read them > > > >>> from the hardware registers if we cannot ensure the BAM hardware is up when > > > >>> the device is being probed. > > > >>> > > > >>> This has often been forgotten when adding new SoC device trees, so make > > > >>> this clear by describing this requirement in the schema. > > > >>> > > > >>> Signed-off-by: Stephan Gerhold <stephan.gerhold@xxxxxxxxxx> > > > >>> --- > > > >>> Documentation/devicetree/bindings/dma/qcom,bam-dma.yaml | 4 ++++ > > > >>> 1 file changed, 4 insertions(+) > > > >>> > > > >>> diff --git a/Documentation/devicetree/bindings/dma/qcom,bam-dma.yaml b/Documentation/devicetree/bindings/dma/qcom,bam-dma.yaml > > > >>> index 3ad0d9b1fbc5e4f83dd316d1ad79773c288748ba..5f7e7763615578717651014cfd52745ea2132115 100644 > > > >>> --- a/Documentation/devicetree/bindings/dma/qcom,bam-dma.yaml > > > >>> +++ b/Documentation/devicetree/bindings/dma/qcom,bam-dma.yaml > > > >>> @@ -90,8 +90,12 @@ required: > > > >>> anyOf: > > > >>> - required: > > > >>> - qcom,powered-remotely > > > >>> + - num-channels > > > >>> + - qcom,num-ees > > > >>> - required: > > > >>> - qcom,controlled-remotely > > > >>> + - num-channels > > > >>> + - qcom,num-ees > > > >> > > > >> I think I'd rather see these deprecated and add the clock everywhere.. > > > >> Do we know which one we need to add on newer platforms? Or maybe it's > > > >> been transformed into an icc path? > > > > > > > > This isn't feasible, there are too many different setups. Also often the > > > > BAM power management is tightly integrated into the consumer interface. > > > > To give a short excerpt (I'm sure there are even more obscure uses): > > > > > > > > - BLSP BAM (UART, I2C, SPI on older SoCs): > > > > 1. Enable GCC_BLSP_AHB_CLK > > > > -> This is what the bam_dma driver supports currently. > > > > > > > > - Crypto BAM: Either > > > > OR 1. Vote for single RPM clock > > > > OR 1. Enable 3 separate clocks (CE, CE_AHB, CE_AXI) > > > > OR 1. Vote dummy bandwidth for interconnect > > > > > > > > - BAM DMUX (WWAN on older SoCs): > > > > 1. Start modem firmware > > > > 2. Wait for BAM DMUX service to be up > > > > 3. Vote for power up via the BAM-DMUX-specific SMEM state > > > > 4. Hope the firmware agrees and brings up the BAM > > > > > > > > - SLIMbus BAM (audio on some SoCs): > > > > 1. Start ADSP firmware > > > > 2. Wait for QMI SLIMBUS service to be up via QRTR > > > > 3. Vote for power up via SLIMbus-specific QMI messages > > > > 4. Hope the firmware agrees and brings up the BAM > > > > > > > > Especially for the last two, we can't implement support for those > > > > consumer-specific interfaces in the BAM driver. Implementing support for > > > > the 3 variants of the Crypto BAM would be possible, but it's honestly > > > > the least interesting use case of all these. It's not really clear why > > > > we are bothing with the crypto engine on newer SoCs at all, see e.g. [1]. > > > > > > > > [1]: https://lore.kernel.org/linux-arm-msm/20250118080604.GA721573@sol.localdomain/ > > > > > > > >> Reading back things from this piece of HW only to add it to DT to avoid > > > >> reading it later is a really messy solution. > > > > > > > > In retrospect, it could have been cleaner to avoid describing the BAM as > > > > device node independent of the consumer. We wouldn't have this problem > > > > if the BAM driver would only probe when the consumer is already ready. > > > > > > > > But I think specifying num-channels in the device tree is the cleanest > > > > way out of this mess. I have a second patch series ready that drops > > > > qcom,num-ees and validates the num-channels once it's safe reading from > > > > the BAM registers. That way, you just need one boot test to ensure the > > > > device tree description is really correct. > > > > > > Thanks for the detailed explanation! > > > > > > Do you think it could maybe make sense to expose a clock/power-domain > > > from the modem/adsp rproc and feed it to the DMUX / SLIM instances when > > > an appropriate ping arrives? This way we'd also defer probing the drivers > > > until the device is actually accessible. > > > > > > > Maybe, but that would result in a cyclic dependency between the DMA > > provider and consumer. E.g. > > > > bam_dmux_dma: dma-controller@ { > > #dma-cells = <1>; > > power-domains = <&bam_dmux>; > > }; > > > > remoteproc@ { > > /* ... */ > > > > bam_dmux: bam-dmux { > > dmas = <&bam_dmux_dma 4>, <&bam_dmux_dma 5>; > > dma-names = "tx", "rx"; > > }; > > }; > > > > fw_devlink will likely get confused by that. > > Why? We have a property to break cycles: post-init-providers > > That doesn't work here? > Thanks, I was not aware of that property. This looks quite useful for fixing up some of the other cyclic dependencies we have! Nevertheless, for this specific case, I still think we should not make such large breaking changes at this point. As I pointed out further below in my quoted email, this is a legacy hardware block that will likely not get any major new users in the future. We're essentially discussing to rework several bindings and drivers just to drop a single straightforward "num-channels = <N>" property. A property that we will need to keep support for anyway, to support users with older DTBs. This effort (and risk) is really better spent elsewhere. Thanks, Stephan
