Re: Problem of initialization of platform-ehci-usb in sbsa-ref

[Yuquan Wang]

> On 2023-04-25 16:34:04, Peter Maydell replied:
> 
> On Mon, 24 Apr 2023 at 13:33, 王宇泉 <wangyuquan1236@phytium.com.cn> wrote:
> > As a junior OS engineer, I met a problem of initialization of 
> > platform-ehci-usb in sbsa-ref recently.
> >
> > The result of sbsa-acs(UEFI Shell application) on sbsa-ref shows that 
> > "Peripheral: Num of USB controllers: 0".
> >
> > And I found that the platform-ehci-usb in qemu is a 32-bits DMA device 
> > while our sbsa-ref machine does not own
> >
> > DRAM memory below 4G. It seems like a contradiction point.
> 
> This definitely doesn't seem like an intentional thing.
> What specifically do you mean by "32-bits DMA device" ?
> Is our implementation of this device accidentally not
> handling addresses above 4GB? Or is the specification of
> the device itself limited to 4GB addresses? Or is this a
> guest driver problem?
> 
> thanks
> -- PMM

Hi, 

Maybe the specific explanation is that qemu implements that:
In hw/usb/hcd-ehci.c:
void usb_ehci_init(EHCIState *s, DeviceState *dev)
{
...
"s->caps[0x08] = 0x80;"

According to EHCI spec version 1.0 Section 2.2.4,
the set of "0x80" on Host Controller Capability Parameters 
Register means this(qemu) EHCI Host Controller does not have 
64-bit Addressing Capability. So, I think above information 
can prove that our implementation of this device can not 
handle addresses above 4GB without the help of SMMU.

Thanks
Yuquan


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