On Wed, Aug 23, 2023 at 2:26 PM Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx> wrote: > > On Wed, Aug 23, 2023 at 06:29:08PM +0200, Lorenzo Pieralisi wrote: > > On Wed, Aug 23, 2023 at 09:48:40AM -0500, Rob Herring wrote: > > > On Wed, Aug 23, 2023 at 2:30 AM Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx> wrote: > > > > > > > > On Mon, Aug 21, 2023 at 12:01:50PM -0400, Jim Quinlan wrote: > > > > > On Mon, Aug 21, 2023 at 11:41 AM Lorenzo Pieralisi > > > > > <lpieralisi@xxxxxxxxxx> wrote: > > > > > > > > > > > > On Mon, Aug 21, 2023 at 11:25:11AM -0400, Jim Quinlan wrote: > > > > > > > On Mon, Aug 21, 2023 at 10:47 AM Lorenzo Pieralisi > > > > > > > <lpieralisi@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > On Fri, Jun 23, 2023 at 10:40:54AM -0400, Jim Quinlan wrote: > > > > > > > > > This commit adds the boolean "brcm,enable-l1ss" property: > > > > > > > > > > > > > > > > > > The Broadcom STB/CM PCIe HW -- a core that is also used by RPi SOCs -- > > > > > > > > > requires the driver probe() to deliberately place the HW one of three > > > > > > > > > CLKREQ# modes: > > > > > > > > > > > > > > > > > > (a) CLKREQ# driven by the RC unconditionally > > > > > > > > > (b) CLKREQ# driven by the EP for ASPM L0s, L1 > > > > > > > > > (c) Bidirectional CLKREQ#, as used for L1 Substates (L1SS). > > > > > > > > > > > > > > > > > > The HW+driver can tell the difference between downstream devices that > > > > > > > > > need (a) and (b), but does not know when to configure (c). All devices > > > > > > > > > should work fine when the driver chooses (a) or (b), but (c) may be > > > > > > > > > desired to realize the extra power savings that L1SS offers. So we > > > > > > > > > introduce the boolean "brcm,enable-l1ss" property to inform the driver > > > > > > > > > that (c) is desired. Setting this property only makes sense when the > > > > > > > > > downstream device is L1SS-capable and the OS is configured to activate > > > > > > > > > this mode (e.g. policy==powersupersave). > > > > > > > > > > > > > > > > > > This property is already present in the Raspian version of Linux, but the > > > > > > > > > upstream driver implementation that follows adds more details and > > > > > > > > > discerns between (a) and (b). > > > > > > > > > > > > > > > > > > Signed-off-by: Jim Quinlan <james.quinlan@xxxxxxxxxxxx> > > > > > > > > > Reviewed-by: Rob Herring <robh@xxxxxxxxxx> > > > > > > > > > --- > > > > > > > > > Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml | 9 +++++++++ > > > > > > > > > 1 file changed, 9 insertions(+) > > > > > > > > > > > > > > > > > > diff --git a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml > > > > > > > > > index 7e15aae7d69e..8b61c2179608 100644 > > > > > > > > > --- a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml > > > > > > > > > +++ b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml > > > > > > > > > @@ -64,6 +64,15 @@ properties: > > > > > > > > > > > > > > > > > > aspm-no-l0s: true > > > > > > > > > > > > > > > > > > + brcm,enable-l1ss: > > > > > > > > > + description: Indicates that PCIe L1SS power savings > > > > > > > > > + are desired, the downstream device is L1SS-capable, and the > > > > > > > > > + OS has been configured to enable this mode. For boards > > > > > > > > > > > > > > > > What does this mean ? I don't think DT properties are supposed > > > > > > > > to carry information related to how the OS is configured. > > > > > > > > > > > > > > The DT setting in question is unrelated to the statement "and the OS > > > > > > > has been configured to > > > > > > > enable this mode". > > > > > > > > > > > > > > This is merely saying that even if you enable "brcm,l1ss-enable" > > > > > > > that you may not get L1SS power savings w/o setting > > > > > > > "CONFIG_PCIEASPM_POWER_SUPERSAVE=y". > > > > > > > I mentioned that exact term but a reviewer nakked it because > > > > > > > apparently DT descriptions should not be OS specific. > > > > > > Yeah, probably the OS part should be dropped. > > > > I will drop it - if you don't mind. > > > > > > > > > I am actually open for this to be a command-line option but I wanted to honor > > > > > > > what the Raspian OS folks have already done. RaspianOS already has > > > > > > > "brcm,enable-l1ss" > > > > > > > set in their DTS files. > > > > > > > > > > > > This is about the mainline kernel, I don't have any visibility into > > > > > > downstream kernels (where that property management was added without DT > > > > > > and PCI maintainers supervision). > > > > > > > > > > > > Raspian OS folks' choice is theirs but it can't and it shouldn't override > > > > > > the mainline review process even though I understand the position you > > > > > > are in. > > > > > > Sure, but we shouldn't change things just to be different from > > > downstream. If we're only discussing the color of the shed, then no > > > point changing it. > > > > Sure, no problem. > > > > > > > Understood, but using the command line has its warts as well; I now recall the > > > > > discussion Bjorn and I had regarding this option. I'm pretty sure > > > > > that upstreaam will not allow the following > > > > > possible command line kernel params: > > > > > > > > > > brcm,enable-l1ss > > > > > pci=brcm,entable-l1ss > > > > > > > > > > Bjorn suggested using the documented but (IMO) obscure and rarely > > > > > used format > > > > > > > > > > pci=[<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*pci:<vendor>:<device>[:<subvendor>:<subdevice>] > > > > > > > > > > but this is just going in the wrong direction; here's why. Using the > > > > > above iformat s completely dependent on the > > > > > PCI "linux-domaiin" property, a non-HW related DT property I might > > > > > add. Since "linux-domain" is already > > > > > a valid and well-used DT property, and the value of the above > > > > > command line format is dependent > > > > > on the value of the "linux-domain", why not be consistent and let > > > > > "brcm,enable-l1ss" be a Broadcom specific property? > > > > > > > > I am just asking to add a module_param to the host controller driver. > > > > > > FWIW, gregkh pretty much always nacks new module parameters. > > > > Fine by me. > > > > > > Anyway - time is running out for v6.6, I need Rob's feedback, if I don't > > > > hear from him today I will merge the last three patches and postpone the > > > > discussion. > > > > > > You've already got my reviewed-by. If you aren't happy with this, then > > > fine. I don't know enough about L1SS to comment further. Is it > > > normally always supported or discoverable? If so, then I'd think we'd > > > want it default enabled with a disable override flag. Maybe it should > > > be generic? > > > > It is not that I am not happy with it - we asked questions to understand > > what this property was for, I think that's normal. > > > > I will merge this series as-is. > > > > There is a discussion ongoing here: https://lore.kernel.org/linux-pci/20230823181650.GL3737@thinkpad/T/#u > > Can you please hold on to merging this series until we've reached a conclusion? (2) There are odd boards out there which TL;DR: I'm okay with postponing the two clkreq# commits. Sigh. I really wish we had this discussion months ago when this series was submitted. I do think the best -- but not perfect -- way to do this is with a DT param. AFAICT there is no way to do this with a command line param with it being accepted, module_param or otherwise; please see my reasons from this thread. Also, Rob just said that GregH will probably reject a new module_param anyway. That being said, the recent discussions are insightful and have me reconsidering having the "l1ss mode" be the default -- it has certainly worked well for the RaspianOS folks. That being said, the RaspianOS folks do not experience the flavor of form-factors and devices as Broadcom STB, and the admonitions of our HW designer are of great concern to me. In light of the above I am okay with postponing the two clkreq-related commits to avoid any missteps. Regards, Jim > > - Mani > > > Lorenzo > > -- > மணிவண்ணன் சதாசிவம்
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