RE: [PATCH v18 09/20] PCI: dwc: Add PCI_EXP_LNKCAP_MLW handling

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Hi Manivannan,

> From: Manivannan Sadhasivam, Sent: Monday, July 24, 2023 8:04 PM
> 
> Subject should contain the word "missing". Like, "Add missing PCI_EXP_LNKCAP_MLW
> handling".

I got it.

> On Fri, Jul 21, 2023 at 04:44:41PM +0900, Yoshihiro Shimoda wrote:
> > Update dw_pcie_link_set_max_link_width() to set PCI_EXP_LNKCAP_MLW.
> > In accordance with the DW PCIe RC/EP HW manuals [1,2,3,...] aside with
> > the PORT_LINK_CTRL_OFF.LINK_CAPABLE and GEN2_CTRL_OFF.NUM_OF_LANES[8:0]
> > field there is another one which needs to be updated. It's
> > LINK_CAPABILITIES_REG.PCIE_CAP_MAX_LINK_WIDTH. If it isn't done at
> > the very least the maximum link-width capability CSR won't expose
> > the actual maximum capability.
> >
> > [1] DesignWare Cores PCI Express Controller Databook - DWC PCIe Root Port,
> >     Version 4.60a, March 2015, p.1032
> > [2] DesignWare Cores PCI Express Controller Databook - DWC PCIe Root Port,
> >     Version 4.70a, March 2016, p.1065
> > [3] DesignWare Cores PCI Express Controller Databook - DWC PCIe Root Port,
> >     Version 4.90a, March 2016, p.1057
> > ...
> > [X] DesignWare Cores PCI Express Controller Databook - DWC PCIe Endpoint,
> >       Version 5.40a, March 2019, p.1396
> > [X+1] DesignWare Cores PCI Express Controller Databook - DWC PCIe Root Port,
> >       Version 5.40a, March 2019, p.1266
> >
> > Suggested-by: Serge Semin <fancer.lancer@xxxxxxxxx>
> 
> Add Reported-by also?

I don't think so because Serge suggested the commit description from my submitted patch [1].

[1]
https://lore.kernel.org/linux-pci/20230322065701.po7owyzwisntalyz@mobilestation/

> > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> 
> This looks like a potential bug fix to me. So please move this change before the
> previous patch that introduces dw_pcie_link_set_max_link_width(), tag fixes and
> CC stable list for backporting.

I think that this patch should be a next branch because this is possible to
cause side effective. Almost all drivers/pcie/controller/dwc/ host drivers except
pcie-tegra194.c doesn't have this setting, but I assume that the drivers work correctly
without this setting.

Also, to be honest, I could not find a suitable commit ID for this patch's "Fixes" tag.
Additionally, I could not determine which old kernel versions should have this patch
applied as backporting.

Best regards,
Yoshihiro Shimoda

> - Mani
> 
> > Reviewed-by: Serge Semin <fancer.lancer@xxxxxxxxx>
> > ---
> >  drivers/pci/controller/dwc/pcie-designware.c | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > index 5cca34140d2a..c4998194fe74 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > @@ -730,7 +730,8 @@ static void dw_pcie_link_set_max_speed(struct dw_pcie *pci, u32 link_gen)
> >
> >  static void dw_pcie_link_set_max_link_width(struct dw_pcie *pci, u32 num_lanes)
> >  {
> > -	u32 lwsc, plc;
> > +	u32 lnkcap, lwsc, plc;
> > +	u8 cap;
> >
> >  	if (!num_lanes)
> >  		return;
> > @@ -766,6 +767,12 @@ static void dw_pcie_link_set_max_link_width(struct dw_pcie *pci, u32 num_lanes)
> >  	}
> >  	dw_pcie_writel_dbi(pci, PCIE_PORT_LINK_CONTROL, plc);
> >  	dw_pcie_writel_dbi(pci, PCIE_LINK_WIDTH_SPEED_CONTROL, lwsc);
> > +
> > +	cap = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> > +	lnkcap = dw_pcie_readl_dbi(pci, cap + PCI_EXP_LNKCAP);
> > +	lnkcap &= ~PCI_EXP_LNKCAP_MLW;
> > +	lnkcap |= FIELD_PREP(PCI_EXP_LNKCAP_MLW, num_lanes);
> > +	dw_pcie_writel_dbi(pci, cap + PCI_EXP_LNKCAP, lnkcap);
> >  }
> >
> >  void dw_pcie_iatu_detect(struct dw_pcie *pci)
> > --
> > 2.25.1
> >
> 
> --
> மணிவண்ணன் சதாசிவம்




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