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Message-ID: <fb17e142-e66f-85a7-353c-0e498892b884@quicinc.com>
Date: Tue, 24 Dec 2024 16:05:58 +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 3:25 PM, Dmitry Baryshkov wrote:
> On Tue, Dec 24, 2024 at 02:47:00PM +0530, Krishna Chaitanya Chundru wrote:
>>
>>
>> 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;
>> }
>
> This looks like 'presets->eq_presets[i] = temp;', but I won't insist on
> that.
>
> Also, a strange thought came to my mind: we know that there won't be
> more than 16 lanes. Can we have the following structure instead:
>
> #define MAX_LANES 16
> enum pcie_gts {
> PCIE_GTS_16GTS,
> PCIE_GTS_32GTS,
> PCIE_GTS_64GTS,
> PCIE_GTS_MAX,
> };
> struct pci_eq_presets {
> u16 eq_presets_8gts[MAX_LANES];
> u8 eq_presets_Ngts[PCIE_GTS_MAX][MAX_LANES];
> };
>
> This should allow you to drop the of_property_present() and
> devm_kzalloc(). Just read DT data into a corresponding array.
>
in the dwc driver patch I was using pointers and memory allocation
to known if the property is present or not. If I use this way I might
end up reading dt property again. I think better to switch to have a
array for above 16gts.
- Krishna Chaitanya.
>> }
>> }
>> - Krishna Chaitanya.
>>
>>>
>
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