Re: [PATCH v2 3/3] dwc: PCI: intel: Intel PCIe RC controller driver

Martin Blumenstingl
2019-08-27T20:39:05Z

Hello,

On Tue, Aug 27, 2019 at 5:09 AM Chuan Hua, Lei
<chuanhua.lei@linux.intel.com> wrote:
>
> Hi Martin,
>
> Thanks for your feedback. Please check the comments below.
>
> On 8/27/2019 5:15 AM, Martin Blumenstingl wrote:
> > Hello,
> >
> > On Mon, Aug 26, 2019 at 5:31 AM Chuan Hua, Lei
> > <chuanhua.lei@linux.intel.com> wrote:
> >> Hi Martin,
> >>
> >> Thanks for your valuable comments. I reply some of them as below.
> > you're welcome
> >
> > [...]
> >>>> +config PCIE_INTEL_AXI
> >>>> + bool "Intel AHB/AXI PCIe host controller support"
> >>> I believe that this is mostly the same IP block as it's used in Lantiq
> >>> (xDSL) VRX200 SoCs (with MIPS cores) which was introduced in 2010
> >>> (before Intel acquired Lantiq).
> >>> This is why I would have personally called the driver PCIE_LANTIQ
> >> VRX200 SoC(internally called VR9) was the first PCIe SoC product which
> >> was using synopsys
> >>
> >> controller v3.30a. It only supports PCIe Gen1.1/1.0. The phy is internal
> >> phy from infineon.
> > thank you for these details
> > I wasn't aware that the PCIe PHY on these SoCs was developed by
> > Infineon nor is the DWC version documented anywhere
>
> VRX200/ARX300 PHY is internal value. There are a lot of hardcode which was
> from hardware people. From XRX500, we switch to synopsis PHY. However, later
> comboPHY is coming to the picture. Even though we have one same controller
> with different versions, we most likely will have three different phy
> drivers.
that is a good argument for using a separate PHY driver and
integrating that using the PHY subsystem (which is already the case in
this patch revision)

> > [...]
> >>>> +#define PCIE_CCRID 0x8
> >>>> +
> >>>> +#define PCIE_LCAP 0x7C
> >>>> +#define PCIE_LCAP_MAX_LINK_SPEED GENMASK(3, 0)
> >>>> +#define PCIE_LCAP_MAX_LENGTH_WIDTH GENMASK(9, 4)
> >>>> +
> >>>> +/* Link Control and Status Register */
> >>>> +#define PCIE_LCTLSTS 0x80
> >>>> +#define PCIE_LCTLSTS_ASPM_ENABLE GENMASK(1, 0)
> >>>> +#define PCIE_LCTLSTS_RCB128 BIT(3)
> >>>> +#define PCIE_LCTLSTS_LINK_DISABLE BIT(4)
> >>>> +#define PCIE_LCTLSTS_COM_CLK_CFG BIT(6)
> >>>> +#define PCIE_LCTLSTS_HW_AW_DIS BIT(9)
> >>>> +#define PCIE_LCTLSTS_LINK_SPEED GENMASK(19, 16)
> >>>> +#define PCIE_LCTLSTS_NEGOTIATED_LINK_WIDTH GENMASK(25, 20)
> >>>> +#define PCIE_LCTLSTS_SLOT_CLK_CFG BIT(28)
> >>>> +
> >>>> +#define PCIE_LCTLSTS2 0xA0
> >>>> +#define PCIE_LCTLSTS2_TGT_LINK_SPEED GENMASK(3, 0)
> >>>> +#define PCIE_LCTLSTS2_TGT_LINK_SPEED_25GT 0x1
> >>>> +#define PCIE_LCTLSTS2_TGT_LINK_SPEED_5GT 0x2
> >>>> +#define PCIE_LCTLSTS2_TGT_LINK_SPEED_8GT 0x3
> >>>> +#define PCIE_LCTLSTS2_TGT_LINK_SPEED_16GT 0x4
> >>>> +#define PCIE_LCTLSTS2_HW_AUTO_DIS BIT(5)
> >>>> +
> >>>> +/* Ack Frequency Register */
> >>>> +#define PCIE_AFR 0x70C
> >>>> +#define PCIE_AFR_FTS_NUM GENMASK(15, 8)
> >>>> +#define PCIE_AFR_COM_FTS_NUM GENMASK(23, 16)
> >>>> +#define PCIE_AFR_GEN12_FTS_NUM_DFT (SZ_128 - 1)
> >>>> +#define PCIE_AFR_GEN3_FTS_NUM_DFT 180
> >>>> +#define PCIE_AFR_GEN4_FTS_NUM_DFT 196
> >>>> +
> >>>> +#define PCIE_PLCR_DLL_LINK_EN BIT(5)
> >>>> +#define PCIE_PORT_LOGIC_FTS GENMASK(7, 0)
> >>>> +#define PCIE_PORT_LOGIC_DFT_FTS_NUM (SZ_128 - 1)
> >>>> +
> >>>> +#define PCIE_MISC_CTRL 0x8BC
> >>>> +#define PCIE_MISC_CTRL_DBI_RO_WR_EN BIT(0)
> >>>> +
> >>>> +#define PCIE_MULTI_LANE_CTRL 0x8C0
> >>>> +#define PCIE_UPCONFIG_SUPPORT BIT(7)
> >>>> +#define PCIE_DIRECT_LINK_WIDTH_CHANGE BIT(6)
> >>>> +#define PCIE_TARGET_LINK_WIDTH GENMASK(5, 0)
> >>>> +
> >>>> +#define PCIE_IOP_CTRL 0x8C4
> >>>> +#define PCIE_IOP_RX_STANDBY_CTRL GENMASK(6, 0)
> >> no need for IOP
> > with "are you sure that you need any of the registers above?" I really
> > meant all registers above (including, but not limited to IOP)
> >
> > [...]
> >> As I mentioned, VRX200 was a very old PCIe Gen1.1 product. In our latest
> >> SoC Lightning
> >>
> >> Mountain, we are using synopsys controller 5.20/5.50a. We support
> >> Gen2(XRX350/550),
> >>
> >> Gen3(PRX300) and GEN4(X86 based SoC). We also supported dual lane and
> >> single lane.
> >>
> >> Some of the above registers are needed to control FTS, link width and
> >> link speed.
> > only now I noticed that I didn't explain why I was asking whether all
> > these registers are needed
> > my understanding of the DWC PCIe controller driver "library" is that:
> > - all functionality which is provided by the DesignWare PCIe core
> > should be added to drivers/pci/controller/dwc/pcie-designware*
> > - functionality which is built on top/around the DWC PCIe core should
> > be added to <vendor specific driver>
> >
> > the link width and link speed settings (I don't know about "FTS")
> > don't seem Intel/Lantiq controller specific to me
> > so the register setup for these bits should be moved to
> > drivers/pci/controller/dwc/pcie-designware*
>
> FTS means fast training sequence. Different generations will have
> different FTS. Common DWC drivers have default number for all generations
> which are not optimized.
I am not a DWC PCIe driver expert, but it seems to me that this is
exactly the reason why struct dw_pcie has a "version" field (which
you're also filling).
same as below: I'm interested in the DWC PCIe maintainer's opinion

> DWC driver handles link speed and link width during the initialization.
> Then left link speed change and link width to device (EP) according to
> PCIe spec. Not sure if other vendors or customers have this kind of
> requirement. We implemented this due to customer's requirement.
>
> We can check with DWC maintainer about this.
thank you for the explanation.
I am also interested in hearing the DWC PCIe maintainer's opinion on this topic

[...]
> > now I am wondering:
> > - if we don't have to disable the interrupt line (once it is enabled),
> > why can't we enable all of these interrupts at initialization time
> > (instead of doing it on-demand)?
> Good point! we even can remote map_irq patch, directly call
> of_irq_parse_and_map_pci as other drivers do.
>
> > - if the interrupts do have to be disabled again (that is what I
> > assumed so far) then where is this supposed to happen? (my solution
> > for this was to implement a simple interrupt controller within the
> > PCIe driver which only supports enable/disable. disclaimer: I didn't
> > ask the PCI or interrupt maintainers for feedback on this yet)
> >
> > [...]
>
> We can implement one interrupt controller, but personally, it has too
> much overhead. If we follow this way, almost all modules of all old
> lantiq SoCs can implement one interrupt controller. Maybe you can check
> with PCI maintainer for their comments.
if we can enable the PCI_INTA/B/C/D interrupts unconditionally then
you can switch to the standard of_irq_parse_and_map_pci implementation
(as you already noted above).
in that case the extra interrupt controller won't be needed.

I have no idea how to test whether unconditionally enabling these
interrupts (in the APP registers that is) causes any problems though.
that's why I went the interrupt-controller route in my experiment.
if the hardware works with a simplified version then I'm more than
happy to use that

[...]
> >>>> +static int intel_pcie_ep_rst_init(struct intel_pcie_port *lpp)
> >>>> +{
> >>>> + struct device *dev = lpp->pci->dev;
> >>>> + int ret = 0;
> >>>> +
> >>>> + lpp->reset_gpio = devm_gpiod_get(dev, "reset", GPIOD_OUT_LOW);
> >>>> + if (IS_ERR(lpp->reset_gpio)) {
> >>>> + ret = PTR_ERR(lpp->reset_gpio);
> >>>> + if (ret != -EPROBE_DEFER)
> >>>> + dev_err(dev, "failed to request PCIe GPIO: %d\n", ret);
> >>>> + return ret;
> >>>> + }
> >>>> + /* Make initial reset last for 100ms */
> >>>> + msleep(100);
> >>> why is there lpp->rst_interval when you hardcode 100ms here?
> >> There are different purpose. rst_interval is purely for asserted reset
> >> pulse.
> >>
> >> Here 100ms is to make sure the initial state keeps at least 100ms, then we
> >> can reset.
> > my interpretation is that it totally depends on the board design or
> > the bootloader setup.
>
> Partially, you are right. However, we should not add some dependency
> here from
> bootloader and board. rst_interval is just to make sure the pulse (low
> active or high active)
> lasts the specified the time.
+Cc Kishon

he recently added support for a GPIO reset line to the
pcie-cadence-host.c [0] and I believe he's also maintaining
pci-keystone.c which are both using a 100uS delay (instead of 100ms).
I don't know the PCIe spec so maybe Kishon can comment on the values
that should be used according to the spec.
if there's then a reason why values other than the ones from the spec
are needed then there should be a comment explaining why different
values are needed (what problem does it solve).

> > on a board where the bootloader initializes the GPIO to logical "0"
> > the devm_gpiod_get() call will not change the GPIO output.
> > in this case a 100ms delay may be OK (based on your description)
> >
> > however, if the GPIO was a logical "1" (for example if the bootloader
> > set it to that value - and considering the GPIOD_OUT_LOW flag) then it
> > will be set to "0" with the devm_gpiod_get() call above.
> > now there is a transition from "deasserted" to "asserted" which does
> > not honor lpp->rst_interval
> >
> > I'm not sure if this is a problem or not - all I know is that I don't
> > fully understand the problem yet
> >>> [...]
> >>>> +static int intel_pcie_setup_irq(struct intel_pcie_port *lpp)
> >>>> +{
> >>>> + struct device *dev = lpp->pci->dev;
> >>>> + struct platform_device *pdev;
> >>>> + char *irq_name;
> >>>> + int irq, ret;
> >>>> +
> >>>> + pdev = to_platform_device(dev);
> >>>> + irq = platform_get_irq(pdev, 0);
> >>>> + if (irq < 0) {
> >>>> + dev_err(dev, "missing sys integrated irq resource\n");
> >>>> + return irq;
> >>>> + }
> >>>> +
> >>>> + irq_name = devm_kasprintf(dev, GFP_KERNEL, "pcie_misc%d", lpp->id);
> >>>> + if (!irq_name) {
> >>>> + dev_err(dev, "failed to alloc irq name\n");
> >>>> + return -ENOMEM;
> >>> you are only requesting one IRQ line for the whole driver. personally
> >>> I would drop the custom irq_name and pass NULL to devm_request_irq
> >>> because that will then fall-back to auto-generating an IRQ name based
> >>> on the devicetree node. I assume it's the same for ACPI but I haven't
> >>> tried that yet.
> >> Not sure I understand what you mean. As you know from the code, we have
> >> lpp->id which means
> >>
> >> we have multiple instances of Root Complex(1,2,3,4,8), so we need this
> >> for identification.
> > sorry, I was wrong with my original statement, the name cannot be NULL
> >
> > I checked the other drivers (meson-gx-mmc and meson-saradc) I had in
> > mind and they use dev_name(&pdev->dev);
> > that will give a unique interrupt name (derived from the devicetree)
> > in /proc/interrupts, for example: c1108680.adc, d0070000.mmc,
> > d0072000.mmc, ...
> >
> > [...]
>
> Right. We also use dev_name in our code. However, some people like numbering
> the interface which is easier for them to remember and discuss. I link id to
> domain so that we can easily know what is wrong once we have issues. When we
> tell the address to hardware people and support staff, they are totally
> lost.
ah, this also explains why linux,pci-domain is a mandatory property
(while it's optional for any other PCIe controller driver that I have
seen so far)

> Again, it is ok to switch to dev_name.
both ways will work, I just wanted to point out that you can achieve a
similar goal with less code.
if the current solution works best for your support team then I'm fine
with that as well

[...]
> >>>> +static void __intel_pcie_remove(struct intel_pcie_port *lpp)
> >>>> +{
> >>>> + pcie_rc_cfg_wr_mask(lpp, PCI_COMMAND_MEMORY | PCI_COMMAND_MASTER,
> >>>> + 0, PCI_COMMAND);
> >>> I expect logic like this to be part of the PCI subsystem in Linux.
> >>> why is this needed?
> >>>
> >>> [...]
> >> bind/unbind case we use this. For extreme cases, we use unbind and bind
> >> to reset
> >> PCI instead of rebooting.
> > OK, but this does not seem Intel/Lantiq specific at all
> > why isn't this managed by either pcie-designware-host.c or the generic
> > PCI/PCIe subsystem in Linux?
>
> I doubt if other RC driver will support bind/unbind. We do have this
> requirement due to power management from WiFi devices.
pcie-designware-host.c will gain .remove() support in Linux 5.4
I don't understand how .remove() and then .probe() again is different
from .unbind() followed by a .bind()

Martin

[0] https://lkml.org/lkml/2019/6/4/626