Re: [PATCH v16 01/22] PCI: Add PCI_EXP_LNKCAP_MLW macros

[Serge Semin <fancer.lancer@gmail.com>]

On Mon, Jun 05, 2023 at 12:14:26AM +0000, Yoshihiro Shimoda wrote:
> Hello Serge,
> 
> > From: Serge Semin, Sent: Monday, June 5, 2023 7:51 AM
> > 
> > On Wed, May 10, 2023 at 03:22:13PM +0900, Yoshihiro Shimoda wrote:
> > > Add macros defining Maximum Link Width bits in Link Capabilities
> > > Register.
> > >
> > > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> > > Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> > 
> > You haven't been using these macros in the following up patches since
> > v9. Why do you keep submitting this change then? I would suggest to
> > drop the patch especially seeing the PCI_EXP_LNKCAP_MLW field directly
> > encodes the link width thus these macros unlikely will be of much use.
> 
> Thank you for your review! You're correct. I didn't realized that
> the macros were not used on the patch series..
> 
> However, I also realized that the patch 11/22 used the PCI_EXP_LNKSTA_NLW_SHIFT
> macro for the PCI_EXP_LNKCAP register. So, I'm thinking that I should modify
> this patch as adding PCI_EXP_LNKCAP_MLW_SHIFT instead. But, what do you think?
> 
> --- on the patch 11/22 ---
> > +	cap = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> > +	val = dw_pcie_readl_dbi(pci, cap + PCI_EXP_LNKCAP);
> > +	val &= ~PCI_EXP_LNKCAP_MLW;
> > +	val |= num_lanes << PCI_EXP_LNKSTA_NLW_SHIFT;
> 
> Perhaps, this should be PCI_EXP_LNKCAP_MLW_SHIFT instead.

I'll get to that patch tomorrow, but in any case there is no need in
defining an additional macro here. There is a handy helper FIELD_PREP()
for that: FIELD_PREP(PCI_EXP_LNKSTA_MLW, num_lanes).

IMO for the same reason the PCI_EXP_LNKSTA_NLW_* macros are
unnecessary and can be easily either dropped or replaced by the
FIELD_{PREP,GET} macros usage.

-Serge(y)

> ---
> 
> Best regards,
> Yoshihiro Shimoda
> 
> > -Serge(y)
> > 
> > > ---
> > >  include/uapi/linux/pci_regs.h | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> > > index dc2000e0fe3a..5d48413ac28f 100644
> > > --- a/include/uapi/linux/pci_regs.h
> > > +++ b/include/uapi/linux/pci_regs.h
> > > @@ -538,6 +538,12 @@
> > >  #define  PCI_EXP_LNKCAP_SLS_16_0GB 0x00000004 /* LNKCAP2 SLS Vector bit 3 */
> > >  #define  PCI_EXP_LNKCAP_SLS_32_0GB 0x00000005 /* LNKCAP2 SLS Vector bit 4 */
> > >  #define  PCI_EXP_LNKCAP_SLS_64_0GB 0x00000006 /* LNKCAP2 SLS Vector bit 5 */
> > > +#define  PCI_EXP_LNKCAP_MLW_X1	0x00000010 /* Maximum Link Width x1 */
> > > +#define  PCI_EXP_LNKCAP_MLW_X2	0x00000020 /* Maximum Link Width x2 */
> > > +#define  PCI_EXP_LNKCAP_MLW_X4	0x00000040 /* Maximum Link Width x4 */
> > > +#define  PCI_EXP_LNKCAP_MLW_X8	0x00000080 /* Maximum Link Width x8 */
> > > +#define  PCI_EXP_LNKCAP_MLW_X12	0x000000c0 /* Maximum Link Width x12 */
> > > +#define  PCI_EXP_LNKCAP_MLW_X16	0x00000100 /* Maximum Link Width x16 */
> > >  #define  PCI_EXP_LNKCAP_MLW	0x000003f0 /* Maximum Link Width */
> > >  #define  PCI_EXP_LNKCAP_ASPMS	0x00000c00 /* ASPM Support */
> > >  #define  PCI_EXP_LNKCAP_ASPM_L0S 0x00000400 /* ASPM L0s Support */
> > > --
> > > 2.25.1
> > >