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

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Wed, Jul 26, 2023 at 02:12:15AM +0000, Yoshihiro Shimoda wrote:
> 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@gmail.com>
> > 
> > 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/
> 

Fine then.

> > > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> > 
> > 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.
> 

Ok. But you can still move this patch as I suggested. If we happen to hit any
issue with this setting, then we can easily revert it.

- Mani

> Best regards,
> Yoshihiro Shimoda
> 
> > - Mani
> > 
> > > Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
> > > ---
> > >  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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