On 24.12.2024 11:57 AM, Dmitry Baryshkov wrote:
> On Tue, 24 Dec 2024 at 12:36, Krishna Chaitanya Chundru
> <quic_krichai@xxxxxxxxxxx> wrote:
>>
>>
>>
>> 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@xxxxxxxxxxxxxxxx>
>>>>>>>>>> ---
>>>>>>>>>> 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@xxxxxxxxxxx/
>>>>>>
>>>>>> 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.
>
> Add foo_valid flags to the struct.
Some(u8)/None would be fitting, but we're not there yet :(
Are all 0x00-0xff(ff) values valid for these presets?
>> I think better to switch to have a
>> array for above 16gts.
>
> Whichever way works for you.
Sorta-answering the earlier email, I have no concerns either
Konrad
