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Message-ID: <49ccd5f2-8524-eba4-25ef-4cdc39edc93b@quicinc.com>
Date: Tue, 24 Dec 2024 14:47:00 +0530
From: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: Konrad Dybcio <konradybcio@...nel.org>,
Krishna Chaitanya Chundru
<krishna.chundru@....qualcomm.com>,
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>
Subject: Re: [PATCH v3 2/4] PCI: of: Add API to retrieve equalization presets
from device tree
On 12/24/2024 12:00 AM, Dmitry Baryshkov wrote:
> On Mon, Dec 23, 2024 at 10:13:29PM +0530, Krishna Chaitanya Chundru wrote:
>>
>>
>> On 12/23/2024 8:56 PM, Dmitry Baryshkov wrote:
>>> On Mon, Dec 23, 2024 at 08:02:23PM +0530, Krishna Chaitanya Chundru wrote:
>>>>
>>>>
>>>> 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.
>>>
>>> Please rewrite this in a cleaner way. The code shouldn't raise
>>> questions.
>>>
>>>>>> + *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.
>>>
>>> Please, don't. They have types. void pointers are for the opaque data.
>>>
>> ok.
>>
>> I think then better to use v1 patch
>> https://lore.kernel.org/all/20241116-presets-v1-2-878a837a4fee@quicinc.com/
>>
>> konrad, any objection on using v1 as that will be cleaner way even if we
>> have some repetitive code.
>
> Konrad had a nice suggestion about using the array of values. Please use
> such an array for 16gts and above. This removes most of repetitive code.
>
I don't feel having array in the preset structure looks good, I have
come up with this logic if you feel it is not so good I will go to the
suggested way by having array for 16gts and above.
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 = EQ_PRESET_TYPE_16GTS; i < EQ_PRESET_TYPE_64GTS; 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;
}
switch (i) {
case EQ_PRESET_TYPE_16GTS:
presets->eq_presets_16gts = temp;
break;
case EQ_PRESET_TYPE_32GTS:
presets->eq_presets_32gts = temp;
break;
case EQ_PRESET_TYPE_64GTS:
presets->eq_presets_64gts = temp;
break;
}
}
}
- Krishna Chaitanya.
>
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