[PATCH v7 0/2] PCI: Configure Root Port MPS during host probing

[PATCH v7 0/2] PCI: Configure Root Port MPS during host probing

[Hans Zhang]

Current PCIe initialization exhibits a key optimization gap: Root Ports
may operate with non-optimal Maximum Payload Size (MPS) settings. While
downstream device configuration is handled during bus enumeration, Root
Port MPS values inherited from firmware or hardware defaults often fail
to utilize the full capabilities supported by controller hardware. This
results in suboptimal data transfer efficiency throughout the PCIe
hierarchy.

This patch series addresses this by:

1. Core PCI enhancement (Patch 1):
- Proactively configures Root Port MPS during host controller probing
- Sets initial MPS to hardware maximum (128 << dev->pcie_mpss)
- Conditional on PCIe bus tuning being enabled (PCIE_BUS_TUNE_OFF unset)
  and not in PCIE_BUS_PEER2PEER mode (which requires default 128 bytes)
- Maintains backward compatibility via PCIE_BUS_TUNE_OFF check
- Preserves standard MPS negotiation during downstream enumeration

2. Driver cleanup (Patch 2):
- Removes redundant MPS configuration from Meson PCIe controller driver
- Functionality is now centralized in PCI core
- Simplifies driver maintenance long-term

---
Changes in v7:
- Exclude PCIE_BUS_PEER2PEER mode from Root Port MPS configuration
- Remove redundant check for upstream bridge (Root Ports don't have one)
- Improve commit message and code comments as per Bjorn.

Changes for v6:
https://patchwork.kernel.org/project/linux-pci/patch/20251104165125.174168-1-18255117159@163.com/

- Modify the commit message and comments. (Bjorn)
- Patch 1/2 code logic: Add !bridge check to configure MPS only for Root Ports
  without an upstream bridge (root bridges), avoiding incorrect handling of
  non-root-bridge Root Ports (Niklas).

Changes for v5:
https://patchwork.kernel.org/project/linux-pci/patch/20250620155507.1022099-1-18255117159@163.com/

- Use pcie_set_mps directly instead of pcie_write_mps.
- The patch 1 commit message were modified.

Changes for v4:
https://patchwork.kernel.org/project/linux-pci/patch/20250510155607.390687-1-18255117159@163.com/

- The patch [v4 1/2] add a comment to explain why it was done this way.
- The patch [v4 2/2] have not been modified.
- Drop patch [v3 3/3]. The Maintainer of the pci-aardvark.c file suggests
  that this patch cannot be submitted. In addition, Mani also suggests
  dropping this patch until this series of issues is resolved.

Changes for v3:
https://patchwork.kernel.org/project/linux-pci/patch/20250506173439.292460-1-18255117159@163.com/

- The new split is patch 2/3 and 3/3.
- Modify the patch 1/3 according to Niklas' suggestion.

Changes for v2:
https://patchwork.kernel.org/project/linux-pci/patch/20250425095708.32662-1-18255117159@163.com/

- According to the Maintainer's suggestion, limit the setting of MPS
  changes to platforms with controller drivers.
- Delete the MPS code set by the SOC manufacturer.
---

Hans Zhang (2):
  PCI: Configure Root Port MPS during host probing
  PCI: dwc: Remove redundant MPS configuration

 drivers/pci/controller/dwc/pci-meson.c | 17 -----------------
 drivers/pci/probe.c                    | 12 ++++++++++++
 2 files changed, 12 insertions(+), 17 deletions(-)


base-commit: 765e56e41a5af2d456ddda6cbd617b9d3295ab4e
-- 
2.34.1


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[PATCH v7 1/2] PCI: Configure Root Port MPS during host probing

[Hans Zhang]

Current PCIe initialization logic may leave Root Ports operating with
non-optimal Maximum Payload Size (MPS) settings. The existing code in
pci_configure_mps() returns early for devices without an upstream bridge
which includes Root Ports, so their MPS values remain at firmware
defaults. This fails to utilize the controller's full capabilities,
leading to suboptimal data transfer efficiency across the PCIe hierarchy.

With this patch, during the host controller probing phase:
- When PCIe bus tuning is enabled (not PCIE_BUS_TUNE_OFF) and not
  PCIE_BUS_PEER2PEER (which requires the default 128 bytes for optimal
  peer-to-peer operation), and
- The device is a Root Port, the Root Port's MPS is set to its maximum
  supported value.

Note that this initial maximum MPS setting may be reduced later, during
downstream device enumeration, if any downstream device does not support
the Root Port's maximum MPS.

This change ensures Root Ports are initialized to their maximum MPS before
downstream devices negotiate MPS, while maintaining backward compatibility
via the PCIE_BUS_TUNE_OFF check and not interfering with the
PCIE_BUS_PEER2PEER strategy.

Suggested-by: Niklas Cassel <cassel@kernel.org>
Suggested-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Hans Zhang <18255117159@163.com>
Tested-by: Mahesh Vaidya <mahesh.vaidya@altera.com>
Tested-by: Shawn Lin <shawn.lin@rock-chips.com>
---
 drivers/pci/probe.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 9cd032dff31e..3970d964d868 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2203,6 +2203,18 @@ static void pci_configure_mps(struct pci_dev *dev)
 		return;
 	}
 
+	/*
+	 * Unless MPS strategy is PCIE_BUS_TUNE_OFF (don't touch MPS at all) or
+	 * PCIE_BUS_PEER2PEER (use minimum MPS for peer-to-peer), set Root Ports'
+	 * MPS to their maximum supported value. Depending on the MPS strategy
+	 * and MPSS of downstream devices, a Root Port's MPS may be reduced
+	 * later during device enumeration.
+	 */
+	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT &&
+	    pcie_bus_config != PCIE_BUS_TUNE_OFF &&
+	    pcie_bus_config != PCIE_BUS_PEER2PEER)
+		pcie_set_mps(dev, 128 << dev->pcie_mpss);
+
 	if (!bridge || !pci_is_pcie(bridge))
 		return;
 
-- 
2.34.1


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[PATCH v7 2/2] PCI: dwc: Remove redundant MPS configuration

[Hans Zhang]

The Meson PCIe controller driver manually configures maximum payload
size (MPS) through meson_set_max_payload, duplicating functionality now
centralized in the PCI core.  Deprecating redundant code simplifies the
driver and aligns it with the consolidated MPS management strategy,
improving long-term maintainability.

Signed-off-by: Hans Zhang <18255117159@163.com>
---
 drivers/pci/controller/dwc/pci-meson.c | 17 -----------------
 1 file changed, 17 deletions(-)

diff --git a/drivers/pci/controller/dwc/pci-meson.c b/drivers/pci/controller/dwc/pci-meson.c
index 787469d1b396..3d12e1a9bb0c 100644
--- a/drivers/pci/controller/dwc/pci-meson.c
+++ b/drivers/pci/controller/dwc/pci-meson.c
@@ -261,22 +261,6 @@ static int meson_size_to_payload(struct meson_pcie *mp, int size)
 	return fls(size) - 8;
 }
 
-static void meson_set_max_payload(struct meson_pcie *mp, int size)
-{
-	struct dw_pcie *pci = &mp->pci;
-	u32 val;
-	u16 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
-	int max_payload_size = meson_size_to_payload(mp, size);
-
-	val = dw_pcie_readl_dbi(pci, offset + PCI_EXP_DEVCTL);
-	val &= ~PCI_EXP_DEVCTL_PAYLOAD;
-	dw_pcie_writel_dbi(pci, offset + PCI_EXP_DEVCTL, val);
-
-	val = dw_pcie_readl_dbi(pci, offset + PCI_EXP_DEVCTL);
-	val |= PCIE_CAP_MAX_PAYLOAD_SIZE(max_payload_size);
-	dw_pcie_writel_dbi(pci, offset + PCI_EXP_DEVCTL, val);
-}
-
 static void meson_set_max_rd_req_size(struct meson_pcie *mp, int size)
 {
 	struct dw_pcie *pci = &mp->pci;
@@ -381,7 +365,6 @@ static int meson_pcie_host_init(struct dw_pcie_rp *pp)
 
 	pp->bridge->ops = &meson_pci_ops;
 
-	meson_set_max_payload(mp, MAX_PAYLOAD_SIZE);
 	meson_set_max_rd_req_size(mp, MAX_READ_REQ_SIZE);
 
 	return 0;
-- 
2.34.1


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Re: [PATCH v7 0/2] PCI: Configure Root Port MPS during host probing

[Ricardo Pardini]

On 27/11/2025 18:09, Hans Zhang wrote:
> Current PCIe initialization exhibits a key optimization gap: Root Ports
> may operate with non-optimal Maximum Payload Size (MPS) settings. While
> downstream device configuration is handled during bus enumeration, Root
> Port MPS values inherited from firmware or hardware defaults often fail
> to utilize the full capabilities supported by controller hardware. This
> results in suboptimal data transfer efficiency throughout the PCIe
> hierarchy.
> 
> This patch series addresses this by:
> 
> 1. Core PCI enhancement (Patch 1):
> - Proactively configures Root Port MPS during host controller probing
> - Sets initial MPS to hardware maximum (128 << dev->pcie_mpss)
> - Conditional on PCIe bus tuning being enabled (PCIE_BUS_TUNE_OFF unset)
>    and not in PCIE_BUS_PEER2PEER mode (which requires default 128 bytes)
> - Maintains backward compatibility via PCIE_BUS_TUNE_OFF check
> - Preserves standard MPS negotiation during downstream enumeration
> 
> 2. Driver cleanup (Patch 2):
> - Removes redundant MPS configuration from Meson PCIe controller driver
> - Functionality is now centralized in PCI core
> - Simplifies driver maintenance long-term
> 
> ---
> Changes in v7:
> - Exclude PCIE_BUS_PEER2PEER mode from Root Port MPS configuration
> - Remove redundant check for upstream bridge (Root Ports don't have one)
> - Improve commit message and code comments as per Bjorn.
Hi Hans,

I've tested on an Odroid-HC4 with a SATA SSD (via an ASM1061) by 
applying your v7 on v6.19-rc3 + Bjorn's 
20251103221930.1831376-1-helgaas@kernel.org ("PCI: meson: Remove 
meson_pcie_link_up() timeout, message, speed check" which is required to 
get the meson PCIe to work at all since 6.18). With that setup I get:

# hdparm --direct -t /dev/sda
  Timing O_DIRECT disk reads: 832 MB in  3.00 seconds = 277.33 MB/sec

I've an identical machine, with a similar disk (even slightly faster, on 
paper), running plain 6.12.y and there I get:

# hdparm --direct -t /dev/sda
  Timing O_DIRECT disk reads: 764 MB in  3.00 seconds = 254.26 MB/sec

I repeated those a few times, not very scientific, I know; but anyway:

Tested-by: Ricardo Pardini <ricardo@pardini.net> # on Odroid-HC4

I've also feedback from another user running with this series with 
success on a different meson PCIe machine, will ask them to TB as well; 
they had reported a significant drop in performance since v6.18 without 
this.

Thanks,
Ricardo

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Re: [PATCH v7 0/2] PCI: Configure Root Port MPS during host probing

[Niklas Cassel]

On Fri, Nov 28, 2025 at 01:09:06AM +0800, Hans Zhang wrote:
> Current PCIe initialization exhibits a key optimization gap: Root Ports
> may operate with non-optimal Maximum Payload Size (MPS) settings. While
> downstream device configuration is handled during bus enumeration, Root
> Port MPS values inherited from firmware or hardware defaults often fail
> to utilize the full capabilities supported by controller hardware. This
> results in suboptimal data transfer efficiency throughout the PCIe
> hierarchy.

Hello PCI maintainers,

any chance for this series to be applied?


Kind regards,
Niklas

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Re: [PATCH v7 0/2] PCI: Configure Root Port MPS during host probing

[Hans Zhang]

On 2025/12/31 10:58, Ricardo Pardini wrote:
> On 27/11/2025 18:09, Hans Zhang wrote:
>> Current PCIe initialization exhibits a key optimization gap: Root Ports
>> may operate with non-optimal Maximum Payload Size (MPS) settings. While
>> downstream device configuration is handled during bus enumeration, Root
>> Port MPS values inherited from firmware or hardware defaults often fail
>> to utilize the full capabilities supported by controller hardware. This
>> results in suboptimal data transfer efficiency throughout the PCIe
>> hierarchy.
>>
>> This patch series addresses this by:
>>
>> 1. Core PCI enhancement (Patch 1):
>> - Proactively configures Root Port MPS during host controller probing
>> - Sets initial MPS to hardware maximum (128 << dev->pcie_mpss)
>> - Conditional on PCIe bus tuning being enabled (PCIE_BUS_TUNE_OFF unset)
>>    and not in PCIE_BUS_PEER2PEER mode (which requires default 128 bytes)
>> - Maintains backward compatibility via PCIE_BUS_TUNE_OFF check
>> - Preserves standard MPS negotiation during downstream enumeration
>>
>> 2. Driver cleanup (Patch 2):
>> - Removes redundant MPS configuration from Meson PCIe controller driver
>> - Functionality is now centralized in PCI core
>> - Simplifies driver maintenance long-term
>>
>> ---
>> Changes in v7:
>> - Exclude PCIE_BUS_PEER2PEER mode from Root Port MPS configuration
>> - Remove redundant check for upstream bridge (Root Ports don't have one)
>> - Improve commit message and code comments as per Bjorn.
> Hi Hans,
> 
> I've tested on an Odroid-HC4 with a SATA SSD (via an ASM1061) by 
> applying your v7 on v6.19-rc3 + Bjorn's 20251103221930.1831376-1- 
> helgaas@kernel.org ("PCI: meson: Remove meson_pcie_link_up() timeout, 
> message, speed check" which is required to get the meson PCIe to work at 
> all since 6.18). With that setup I get:
> 
> # hdparm --direct -t /dev/sda
>   Timing O_DIRECT disk reads: 832 MB in  3.00 seconds = 277.33 MB/sec
> 
> I've an identical machine, with a similar disk (even slightly faster, on 
> paper), running plain 6.12.y and there I get:
> 
> # hdparm --direct -t /dev/sda
>   Timing O_DIRECT disk reads: 764 MB in  3.00 seconds = 254.26 MB/sec
> 
> I repeated those a few times, not very scientific, I know; but anyway:
> 
> Tested-by: Ricardo Pardini <ricardo@pardini.net> # on Odroid-HC4
> 
> I've also feedback from another user running with this series with 
> success on a different meson PCIe machine, will ask them to TB as well; 
> they had reported a significant drop in performance since v6.18 without 
> this.
Hi,

Thank you very much for your test. Let's wait for Bjorn's reply.

Best regards,
Hans

> 
> Thanks,
> Ricardo


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Re: [PATCH v7 0/2] PCI: Configure Root Port MPS during host probing

[Niklas Cassel]

On Sun, Jan 18, 2026 at 09:26:45PM +0800, Hans Zhang wrote:
> On 2025/12/31 10:58, Ricardo Pardini wrote:
> > On 27/11/2025 18:09, Hans Zhang wrote:
> > > Current PCIe initialization exhibits a key optimization gap: Root Ports
> > > may operate with non-optimal Maximum Payload Size (MPS) settings. While
> > > downstream device configuration is handled during bus enumeration, Root
> > > Port MPS values inherited from firmware or hardware defaults often fail
> > > to utilize the full capabilities supported by controller hardware. This
> > > results in suboptimal data transfer efficiency throughout the PCIe
> > > hierarchy.
> > > 
> > > This patch series addresses this by:
> > > 
> > > 1. Core PCI enhancement (Patch 1):
> > > - Proactively configures Root Port MPS during host controller probing
> > > - Sets initial MPS to hardware maximum (128 << dev->pcie_mpss)
> > > - Conditional on PCIe bus tuning being enabled (PCIE_BUS_TUNE_OFF unset)
> > >    and not in PCIE_BUS_PEER2PEER mode (which requires default 128 bytes)
> > > - Maintains backward compatibility via PCIE_BUS_TUNE_OFF check
> > > - Preserves standard MPS negotiation during downstream enumeration
> > > 
> > > 2. Driver cleanup (Patch 2):
> > > - Removes redundant MPS configuration from Meson PCIe controller driver
> > > - Functionality is now centralized in PCI core
> > > - Simplifies driver maintenance long-term
> > > 
> > > ---
> > > Changes in v7:
> > > - Exclude PCIE_BUS_PEER2PEER mode from Root Port MPS configuration
> > > - Remove redundant check for upstream bridge (Root Ports don't have one)
> > > - Improve commit message and code comments as per Bjorn.
> > Hi Hans,
> > 
> > I've tested on an Odroid-HC4 with a SATA SSD (via an ASM1061) by
> > applying your v7 on v6.19-rc3 + Bjorn's 20251103221930.1831376-1-
> > helgaas@kernel.org ("PCI: meson: Remove meson_pcie_link_up() timeout,
> > message, speed check" which is required to get the meson PCIe to work at
> > all since 6.18). With that setup I get:
> > 
> > # hdparm --direct -t /dev/sda
> >   Timing O_DIRECT disk reads: 832 MB in  3.00 seconds = 277.33 MB/sec
> > 
> > I've an identical machine, with a similar disk (even slightly faster, on
> > paper), running plain 6.12.y and there I get:
> > 
> > # hdparm --direct -t /dev/sda
> >   Timing O_DIRECT disk reads: 764 MB in  3.00 seconds = 254.26 MB/sec
> > 
> > I repeated those a few times, not very scientific, I know; but anyway:
> > 
> > Tested-by: Ricardo Pardini <ricardo@pardini.net> # on Odroid-HC4
> > 
> > I've also feedback from another user running with this series with
> > success on a different meson PCIe machine, will ask them to TB as well;
> > they had reported a significant drop in performance since v6.18 without
> > this.
> Hi,
> 
> Thank you very much for your test. Let's wait for Bjorn's reply.

Probably too late for the 6.20 / 7.0 merge window...

But.. it would be nice with some kind of feedback from Bjorn.

Is there any chance that this gets applied for 6.21/7.1 or is there
any fundamental objection against this series?


Kind regards,
Niklas

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