Re: [PATCH v9 0/4] PCI: brcmstb: Configure appropriate HW CLKREQ# mode

Jim Quinlan
2024-04-30T21:02:58Z

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On Wed, Apr 3, 2024 at 5:39 PM Jim Quinlan <james.quinlan@broadcom.com> wrote:
>
> v9 -- v8 was setting an internal bus timeout to accomodate large L1 exit
> latencies. After meeting the PCIe HW team it was revealed that the
> HW default timeout value was set low for the purposes of HW debugging
> convenience; for nominal operation it needs to be set to a higher
> value independent of this submission's purpose. This is now a
> separate commit.

Bjorn,

Did you have some time to look at this? Do you have any comments or questions?

Regards,
Jim Quinlan
Broadcom STB/CM
>
> -- With v8, Bjorne asked what was preventing a device from exceeding the
> time required for the above internal bus timeout. The answer to this
> is for us to set the endpoints' max latency {no-,}snoop value to
> something below this internal timeout value. If the endpoint
> respects this value as it should, it will not send an LTR request
> with a larger latency value and not put itself in a situation
> that requires more latency than is possible for the platform.
>
> Typically, ACPI or FW sets these max latency values. In most of our
> systems we do not have this happening so it is up to the RC driver to
> set these values in the endpoint devices. If the endpoints already
> have non-zero values that are lower than what we are setting, we let
> them be, as it is possible ACPI or FW set them and knows something
> that we do not.
>
> -- The "clkreq" commit has only been changed to remove the code that was
> setting the timeout value, as this code is now its own commit.
>
> v8 -- Un-advertise L1SS capability when in "no-l1ss" mode (Bjorn)
> -- Squashed last two commits of v7 (Bjorn)
> -- Fix DT binding description text wrapping (Bjorn)
> -- Fix incorrect Spec reference (Bjorn)
> s/PCIe Spec/PCIe Express Mini CEM 2.1 specification/
> -- Text substitutions (Bjorn)
> s/WRT/With respect to/
> s/Tclron/T_CLRon/
>
> v7 -- Manivannan Sadhasivam suggested (a) making the property look like a
> network phy-mode and (b) keeping the code simple (not counting clkreq
> signal appearances, un-advertising capabilites, etc). This is
> what I have done. The property is now "brcm,clkreq-mode" and
> the values may be one of "safe", "default", and "no-l1ss". The
> default setting is to employ the most capable power savings mode.
>
> v6 -- No code has been changed.
> -- Changed commit subject and comment in "#PERST" commit (Bjorn, Cyril)
> -- Changed sign-off and author email address for all commits.
> This was due to a change in Broadcom's upstreaming policy.
>
> v5 -- Remove DT property "brcm,completion-timeout-us" from
> "DT bindings" commit. Although this error may be reported
> as a completion timeout, its cause was traced to an
> internal bus timeout which may occur even when there is
> no PCIe access being processed. We set a timeout of four
> seconds only if we are operating in "L1SS CLKREQ#" mode.
> -- Correct CEM 2.0 reference provided by HW engineer,
> s/3.2.5.2.5/3.2.5.2.2/ (Bjorn)
> -- Add newline to dev_info() string (Stefan)
> -- Change variable rval to unsigned (Stefan)
> -- s/implementaion/implementation/ (Bjorn)
> -- s/superpowersave/powersupersave/ (Bjorn)
> -- Slightly modify message on "PERST#" commit.
> -- Rebase to torvalds master
>
> v4 -- New commit that asserts PERST# for 2711/RPi SOCs at PCIe RC
> driver probe() time. This is done in Raspian Linux and its
> absence may be the cause of a failing test case.
> -- New commit that removes stale comment.
>
> v3 -- Rewrote commit msgs and comments refering panics if L1SS
> is enabled/disabled; the code snippet that unadvertises L1SS
> eliminates the panic scenario. (Bjorn)
> -- Add reference for "400ns of CLKREQ# assertion" blurb (Bjorn)
> -- Put binding names in DT commit Subject (Bjorn)
> -- Add a verb to a commit's subject line (Bjorn)
> -- s/accomodat(\w+)/accommodat$1/g (Bjorn)
> -- Rewrote commit msgs and comments refering panics if L1SS
> is enabled/disabled; the code snippet that unadvertises L1SS
> eliminates the panic scenario. (Bjorn)
>
> v2 -- Changed binding property 'brcm,completion-timeout-msec' to
> 'brcm,completion-timeout-us'. (StefanW for standard suffix).
> -- Warn when clamping timeout value, and include clamped
> region in message. Also add min and max in YAML. (StefanW)
> -- Qualify description of "brcm,completion-timeout-us" so that
> it refers to PCIe transactions. (StefanW)
> -- Remvove mention of Linux specifics in binding description. (StefanW)
> -- s/clkreq#/CLKREQ#/g (Bjorn)
> -- Refactor completion-timeout-us code to compare max and min to
> value given by the property (as opposed to the computed value).
>
> v1 -- The current driver assumes the downstream devices can
> provide CLKREQ# for ASPM. These commits accomodate devices
> w/ or w/o clkreq# and also handle L1SS-capable devices.
>
> -- The Raspian Linux folks have already been using a PCIe RC
> property "brcm,enable-l1ss". These commits use the same
> property, in a backward-compatible manner, and the implementaion
> adds more detail and also automatically identifies devices w/o
> a clkreq# signal, i.e. most devices plugged into an RPi CM4
> IO board.
>
> Jim Quinlan (4):
> dt-bindings: PCI: brcmstb: Add property "brcm,clkreq-mode"
> PCI: brcmstb: Set reasonable value for internal bus timeout
> PCI: brcmstb: Set downstream maximum {no-}snoop LTR values
> PCI: brcmstb: Configure HW CLKREQ# mode appropriate for downstream
> device
>
> .../bindings/pci/brcm,stb-pcie.yaml | 18 ++
> drivers/pci/controller/pcie-brcmstb.c | 161 +++++++++++++++++-
> 2 files changed, 170 insertions(+), 9 deletions(-)
>
>
> base-commit: 9f8413c4a66f2fb776d3dc3c9ed20bf435eb305e
> --
> 2.17.1