Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev

[Felipe Balbi]

Hi,

Arnd Bergmann <arnd@xxxxxxxx> writes:
> On Thursday, September 8, 2016 12:43:06 PM CEST Felipe Balbi wrote:
>> Arnd Bergmann <arnd@xxxxxxxx> writes:
>> > On Thursday, September 8, 2016 11:29:04 AM CEST Felipe Balbi wrote:
>> >> > If we do that, we have to put child devices of the dwc3 devices into
>> >> > the platform glue, and it also breaks those dwc3 devices that don't
>> >> > have a parent driver.
>> >> 
>> >> Well, this is easy to fix:
>> >> 
>> >>         if (dwc->dev->parent) {
>> >>                 dwc->sysdev = dwc->dev->parent;
>> >>         } else {
>> >>                 dev_info(dwc->dev, "Please provide a glue layer!\n");
>> >>                 dwc->sysdev = dwc->dev;
>> >>         }
>> >
>> > I don't understand. Do you mean we should have an extra level of
>> > stacking and splitting "static struct platform_driver dwc3_driver"
>> > in two so instead of
>> >
>> >       "qcom,dwc3" -> "snps,dwc3" (usb_bus.sysdev) -> "xhci" (usb_bus.dev)
>> >
>> > we do this?
>> >
>> >       "qcom,dwc3" -> "snps,dwc3" (usb_bus.sysdev) -> "dwc3-glue" -> "xhci" (usb_bus.dev)
>> 
>> no 
>> 
>> If we have a parent device, use that as sysdev, otherwise use self as
>> sysdev.
>
> But there is often a parent device in DT, as the xhci device is
> attached to some internal bus that gets turned into a platform_device
> as well, so checking whether there is a parent will get the wrong
> device node.

oh, that makes things more interesting :-s

>> > That sounds a bit clumsy for the sake of consistency with PCI.
>> > The advantage is that xhci can always use the grandparent device
>> > as sysdev whenever it isn't probed through PCI or firmware
>> > itself, but the purpose of the dwc3-glue is otherwise questionable.
>> >
>> > How about adding a 'compatible="snps,dwc3-pci"' property for the dwc3
>> > device when that is created from the PCI driver and checking for that
>> > with the device property interface instead? If it's "snps,dwc3"
>> > we use the device itself while for "snps,dwc3-pci", we use the parent?
>> 
>> Any reason why we wouldn't use e.g. dwc3-omap.dev as sysdev?
>
> That would be incompatible with the USB binding, as the sysdev
> is assumed to be a USB host controller with #address-cells=<1>
> and #size-cells=<0> in order to hold the child devices, for
> example:
>
> / {
>      omap_dwc3_1: omap_dwc3_1@48880000 {
>         compatible = "ti,dwc3";
>         #address-cells = <1>;
>         #size-cells = <1>;
>         ranges;
>         usb1: usb@48890000 {
>                 compatible = "snps,dwc3";
>                 reg = <0x48890000 0x17000>;
>                 #address-cells = <1>;
>                 #size-cells = <0>;
>                 interrupts = <GIC_SPI 71 IRQ_TYPE_LEVEL_HIGH>,
>                              <GIC_SPI 71 IRQ_TYPE_LEVEL_HIGH>,
>                              <GIC_SPI 72 IRQ_TYPE_LEVEL_HIGH>;
>                 interrupt-names = "peripheral",
>                                   "host",
>                                   "otg";
>                 phys = <&usb2_phy1>, <&usb3_phy1>;
>                 phy-names = "usb2-phy", "usb3-phy";
>
>                 hub@1 {
>                         compatible = "usb5e3,608";
>                         reg = <1>;
>                         #address-cells = <1>;
>                         #size-cells = <0>;
>
>                         ethernet@1 {
>                                 compatible = "usb424,ec00";
>                                 mac-address = [00 11 22 33 44 55];
>                                 reg = <1>;
>                         };
>                 };
>         };
> };
>
> It's also the node that contains the "phys" properties and
> presumably other properties like "otg-rev", "maximum-speed"
> etc.
>
> If we make the sysdev point to the parent, then we can no longer
> look up those properties and child devices from the USB core code
> by looking at "sysdev->of_node".

this also makes things more interesting. I can't of anything other than
having some type of flag passed via e.g. device_properties by dwc3-pci.c
:-s

It's quite a hack, though. I still think that inheriting DMA (or
manually initializing a child with parent's DMA bits and pieces) is the
best way to go. So we're back to of_dma_configure() and
acpi_dma_configure(), right?

But this needs to be done before dwc3_probe() executes. For dwc3-pci
that's easy, but for DT devices, seems like it should be in of
core. Below is, clearly, not enough but should show the idea:

diff --git a/drivers/of/device.c b/drivers/of/device.c
index fd5cfad7c403..a54610198946 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -94,8 +94,12 @@ void of_dma_configure(struct device *dev, struct device_node *np)
         * Set default coherent_dma_mask to 32 bit.  Drivers are expected to
         * setup the correct supported mask.
         */
-       if (!dev->coherent_dma_mask)
-               dev->coherent_dma_mask = DMA_BIT_MASK(32);
+       if (!dev->coherent_dma_mask) {
+               if (!dev->parent->coherent_dma_mask)
+                       dev->coherent_dma_mask = DMA_BIT_MASK(32);
+               else
+                       dev->coherent_dma_mask = dev->parent->coherent_dma_mask;
+       }
 
        /*
         * Set it to coherent_dma_mask by default if the architecture


-- 
balbi

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