On Mon, Jul 31, 2023 at 01:15:02AM +0000, Yoshihiro Shimoda wrote:
> Hi Serge,
>
> > From: Serge Semin, Sent: Saturday, July 29, 2023 1:07 AM
> >
> > On Fri, Jul 28, 2023 at 04:19:38AM +0000, Yoshihiro Shimoda wrote:
> > > Hi Manivannan,
> > >
> > > > From: Manivannan Sadhasivam, Sent: Friday, July 28, 2023 11:51 AM
> > > >
> > > > 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@xxxxxxxxx>
> > > > > >
> > > > > > Add Reported-by also?
> > > > >
> > > > > I don't think so because Serge suggested the commit description from my submitted patch [1].
> > > > >
> > > > > [1]
> > > > >
> > > <snip URL>
> > > > >
> > > >
> > > > Fine then.
> > > >
> > > > > > > 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.
> > > > >
> > > >
> >
> > > > 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.
> > >
> > > I got it. I'll move this patch as you suggested.
> >
> > No. By moving this patch to be implemented before the patch:
> > [PATCH v18 08/20] PCI: dwc: Add dw_pcie_link_set_max_link_width()
> > you won't be able to easily revert it afterwards because the patch #8
> > will move the code added by the patch #9 to the
> > dw_pcie_link_set_max_link_width() function. Basically you suggest to
> > switch the preparation and functional patches order which doesn't look
> > right.
>
> You're correct. If moving this patch to the top of this series and then
> still apply the original #8, it's difficult to revert this patch.
>
> > Basically the Link-width-related part of this series currently implies
> > the next logic:
> >
> > 1. Prepare the DW PCIe core driver to implementing a comprehensive
> > Max-link-width setup methods (aka as it's done in
> > dw_pcie_link_set_max_speed()) by moving the Link-width related code to
> > a dedicated method:
> > [PATCH v18 08/20] PCI: dwc: Add dw_pcie_link_set_max_link_width()
> >
> > 2. Add the PCI_EXP_LNKCAP_MLW field update, which
> > dw_pcie_link_set_max_link_width() lacks to be comprehensive:
> > [PATCH v18 09/20] PCI: dwc: Add PCI_EXP_LNKCAP_MLW handling
> >
> > 3. Drop the duplicating code from the Tegra194 PCIe driver:
> > [PATCH v18 10/20] PCI: tegra194: Drop PCI_EXP_LNKSTA_NLW setting
>
> Yes.
>
> > In case if the patch #9 appears to be a bug fix, then it will need to
> > be backported together with patch #8 which isn't a problem at all
> > (though it's doubtfully to happen since nobody reported any problem
> > with that so far).
>
> Basically, I don't think that backporting #8 is good as backport because
> the #8 patch is a clean up code for readability.
>
> > But if patch #9 turns out to break something in
> > current circumstances we'll be able to either easily revert it (since
> > it's applied after the preparation patch) or fix somehow. If you
> > switch patch #8 and #9 order, the reversion will require to be
> > performed for both these patches to avoid the conflicts. Thus I'd
> > suggest to leave the patches order as is which looks more natural and
> > won't cause any problems to revert the functional change or to
> > backport it.
>
> To follow Manivannan's suggestion and your comments, I'm thinking that
> - drop the #8 because this is just clean up code for readability.
> -- After this patch series is merged and worked correctly without any
> regression on other platforms, we can apply the #8.
> - move the #9 to the top of this series as Manivannan suggested.
> -- This mean adding this code into dw_pcie_setup().
>
> But, what do you think?
No. It's better to leave the preparation patch and the order as is.
Once again this patch doesn't look as a bug-fix since nobody reported
any related problem so far. If anyone decides to back it port there
won't a problem with porting both #8 and #9. It's a common practice.
-Serge(y)
>
> Best regards,
> Yoshihiro Shimoda
>
> > -Serge(y)
> >
> > >
> > > Best regards,
> > > Yoshihiro Shimoda
> > >
> > > > - Mani
> > > >
> > > > > 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
> > > >
> > > > --
> > > > மணிவண்ணன் சதாசிவம்
