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.
> I think better to switch to have a
> array for above 16gts.
Whichever way works for you.
>
> - Krishna Chaitanya.
> >> }
> >> }
> >> - Krishna Chaitanya.
> >>
> >>>
> >
--
With best wishes
Dmitry
