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Message-ID: <d317c51a-3913-6c49-f8db-e75589f9289a@quicinc.com>
Date: Mon, 23 Dec 2024 20:02:23 +0530
From: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
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 Wilczyński
<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 12/23/2024 5:17 PM, Dmitry Baryshkov wrote:
> 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.
>
I will update this in next series.
as we are allocating using devm_kzalloc it should be freed on driver
detach, as no special freeing is required.
>> +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.
>
I was trying iterate over each element on the structure as presets holds
the starting address of the structure and to that we are adding size of
the void * point to go to each element. I did this way to reduce the
redundant code to read all the gts which has same way of storing the
data from the device tree. I will add comments here in the next series.
>> + *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*.
>
To have common parsing logic I moved them to void*, as these are
pointers actual memory is allocated by of_pci_get_equalization_presets()
based upon the gts these should not give any issues.
>> +};
>
> Empty lines before and after the struct definition.
>
ack.
- Krishna Chaitanya.
>> #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
>>
>
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