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Message-ID: <piccoomv7rx4dvvfdoesmxbzrdqz4ld6ii6neudsdf4hjj2yzm@2bcuacwa4feb>
Date: Mon, 23 Dec 2024 13:47:10 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: 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>, 
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, Lorenzo Pieralisi <lpieralisi@...nel.org>, 
	Krzysztof WilczyƄski <kw@...ux.com>, linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, konrad.dybcio@....qualcomm.com, 
	quic_mrana@...cinc.com, quic_vbadigan@...cinc.com, 
	Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konradybcio@...nel.org>
Subject: Re: [PATCH v3 2/4] PCI: of: Add API to retrieve equalization presets
 from device tree

On Mon, Dec 23, 2024 at 12:21:15PM +0530, Krishna Chaitanya Chundru wrote:
> PCIe equalization presets are predefined settings used to optimize
> signal integrity by compensating for signal loss and distortion in
> high-speed data transmission.
> 
> As per PCIe spec 6.0.1 revision section 8.3.3.3 & 4.2.4 for data rates
> of 8.0 GT/s, 16.0 GT/s, 32.0 GT/s, and 64.0 GT/s, there is a way to
> configure lane equalization presets for each lane to enhance the PCIe
> link reliability. Each preset value represents a different combination
> of pre-shoot and de-emphasis values. For each data rate, different
> registers are defined: for 8.0 GT/s, registers are defined in section
> 7.7.3.4; for 16.0 GT/s, in section 7.7.5.9, etc. The 8.0 GT/s rate has
> an extra receiver preset hint, requiring 16 bits per lane, while the
> remaining data rates use 8 bits per lane.
> 
> Based on the number of lanes and the supported data rate, this function
> reads the device tree property and stores in the presets structure.
> 
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> ---
>  drivers/pci/of.c  | 45 +++++++++++++++++++++++++++++++++++++++++++++
>  drivers/pci/pci.h | 17 +++++++++++++++--
>  2 files changed, 60 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index dacea3fc5128..99e0e7ae12e9 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -826,3 +826,48 @@ u32 of_pci_get_slot_power_limit(struct device_node *node,
>  	return slot_power_limit_mw;
>  }
>  EXPORT_SYMBOL_GPL(of_pci_get_slot_power_limit);
> +

kerneldoc? Define who should free the memory and how.

> +int of_pci_get_equalization_presets(struct device *dev,
> +				    struct pci_eq_presets *presets,
> +				    int num_lanes)
> +{
> +	char name[20];
> +	void **preset;
> +	void *temp;
> +	int ret;
> +
> +	if (of_property_present(dev->of_node, "eq-presets-8gts")) {
> +		presets->eq_presets_8gts = devm_kzalloc(dev, sizeof(u16) * num_lanes, GFP_KERNEL);
> +		if (!presets->eq_presets_8gts)
> +			return -ENOMEM;
> +
> +		ret = of_property_read_u16_array(dev->of_node, "eq-presets-8gts",
> +						 presets->eq_presets_8gts, num_lanes);
> +		if (ret) {
> +			dev_err(dev, "Error reading eq-presets-8gts %d\n", ret);
> +			return ret;
> +		}
> +	}
> +
> +	for (int i = 1; i < sizeof(struct pci_eq_presets) / sizeof(void *); i++) {
> +		snprintf(name, sizeof(name), "eq-presets-%dgts", 8 << i);
> +		if (of_property_present(dev->of_node, name)) {
> +			temp = devm_kzalloc(dev, sizeof(u8) * num_lanes, GFP_KERNEL);
> +			if (!temp)
> +				return -ENOMEM;
> +
> +			ret = of_property_read_u8_array(dev->of_node, name,
> +							temp, num_lanes);
> +			if (ret) {
> +				dev_err(dev, "Error %s %d\n", name, ret);
> +				return ret;
> +			}
> +
> +			preset = (void **)((u8 *)presets + i * sizeof(void *));

Ugh.

> +			*preset = temp;
> +		}
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(of_pci_get_equalization_presets);
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 14d00ce45bfa..82362d58bedc 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -731,7 +731,12 @@ static inline u64 pci_rebar_size_to_bytes(int size)
>  }
>  
>  struct device_node;
> -
> +struct pci_eq_presets {
> +	void *eq_presets_8gts;
> +	void *eq_presets_16gts;
> +	void *eq_presets_32gts;
> +	void *eq_presets_64gts;

Why are all of those void*? 8gts is u16*, all other are u8*.

> +};

Empty lines before and after the struct definition.

>  #ifdef CONFIG_OF
>  int of_pci_parse_bus_range(struct device_node *node, struct resource *res);
>  int of_get_pci_domain_nr(struct device_node *node);
> @@ -746,7 +751,9 @@ void pci_set_bus_of_node(struct pci_bus *bus);
>  void pci_release_bus_of_node(struct pci_bus *bus);
>  
>  int devm_of_pci_bridge_init(struct device *dev, struct pci_host_bridge *bridge);
> -
> +int of_pci_get_equalization_presets(struct device *dev,
> +				    struct pci_eq_presets *presets,
> +				    int num_lanes);

Keep the empty line.

>  #else
>  static inline int
>  of_pci_parse_bus_range(struct device_node *node, struct resource *res)
> @@ -793,6 +800,12 @@ static inline int devm_of_pci_bridge_init(struct device *dev, struct pci_host_br
>  	return 0;
>  }
>  
> +static inline int of_pci_get_equalization_presets(struct device *dev,
> +						  struct pci_eq_presets *presets,
> +						  int num_lanes)
> +{
> +	return 0;
> +}
>  #endif /* CONFIG_OF */
>  
>  struct of_changeset;
> 
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry

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