linux-kernel - Re: [PATCH v7 2/4] PCI: of: Add API to retrieve equalization presets from device tree

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Message-ID: <20250314150006.crjestg3rtxu726q@thinkpad>
Date: Fri, 14 Mar 2025 20:30:06 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	quic_mrana@...cinc.com, quic_vbadigan@...cinc.com
Subject: Re: [PATCH v7 2/4] PCI: of: Add API to retrieve equalization presets
 from device tree

On Tue, Mar 11, 2025 at 04:31:33PM +0530, Krishna Chaitanya Chundru wrote:

[...]

> > > diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> > > index 01e51db8d285..c8d44b21ef03 100644
> > > --- a/drivers/pci/pci.h
> > > +++ b/drivers/pci/pci.h
> > > @@ -9,6 +9,8 @@ struct pcie_tlp_log;
> > >   /* Number of possible devfns: 0.0 to 1f.7 inclusive */
> > >   #define MAX_NR_DEVFNS 256
> > > +#define MAX_NR_LANES 16
> > > +
> > >   #define PCI_FIND_CAP_TTL	48
> > >   #define PCI_VSEC_ID_INTEL_TBT	0x1234	/* Thunderbolt */
> > > @@ -808,6 +810,20 @@ static inline u64 pci_rebar_size_to_bytes(int size)
> > >   struct device_node;
> > > +#define PCI_EQ_RESV	0xff
> > > +
> > > +enum equalization_preset_type {
> > 
> > For the sake of completeness, you should add EQ_PRESET_TYPE_8GTS also. You could
> > skip it while reading the of_property_read_u8_array().
> Can we add like this to make parsing logic easier otherwise while
> deference the presets array we need to subtract -1.

Without EQ_PRESET_TYPE_8GTS, it would look like a missing enum. So someone will
add EQ_PRESET_TYPE_8GTS in the future and it will break the driver. So be
prepared for it. 

> currently we are using like this presets[EQ_PRESET_TYPE_16GTS] if
> we want to keep in same way we need to use like below.
> 
> 	EQ_PRESET_TYPE_8GTS,
> 	EQ_PRESET_TYPE_16GTS = 0,

No. First enum element should be initialized with 0.

- Mani

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