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

[Jim Quinlan]

On Wed, Apr 3, 2024 at 5:39 PM Jim Quinlan <james.quinlan@xxxxxxxxxxxx> 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
>

Attachment: smime.p7s
Description: S/MIME Cryptographic Signature