Re: [Bug] Bring up Dom0 on Arm board

[Julien Grall <julien@xxxxxxx>]

On 16/01/2023 05:59, 蔡力刚 wrote:
> Hi,
Hi,

> > >  About the mali and sdmmc drivers problem, I compare the log between boot with xen and boot without xen.
> > >  And found an error log as below:
> > >  [ 65.517345] arm-scmi firmware:scmi: SCMI Notifications - Core Enabled.
> > >  (XEN) d0v2 Unhandled SMC/HVC: 0x82000010
> > >  [ 66.559382] arm-scmi firmware:scmi: unable to communicate with SCMI
> > >  [ 66.559516] arm-scmi: probe of firmware:scmi failed with error -95
> > >  It seems SCMI driver probe failed.
> > >  So I did an experiment, disable SCMI driver and rebuild the Linux kernel,
> > >  boot up in normal way without xen, and reproduces the problem that mali and sdmmc did not bring up.
> > >  It looks like a high probability SCMI cause the problem.
> > >  I read the Linux code and targeting located the error -95,
> > >  It seems SCMI probe failed cause by SMCCC not supported, code as below:
> > >  static int smc_send_message(struct scmi_chan_info *cinfo,
> > >    struct scmi_xfer *xfer)
> > >  {
> > >    struct scmi_smc *scmi_info = cinfo->transport_info;
> > >    struct arm_smccc_res res;
> > >    mutex_lock(&scmi_info->shmem_lock);
> > >    shmem_tx_prepare(scmi_info->shmem, xfer);
> > >    if (scmi_info->irq)
> > >    reinit_completion(&scmi_info->tx_complete);
> > >    arm_smccc_1_1_invoke(scmi_info->func_id, 0, 0, 0, 0, 0, 0, 0, &res);
> > >    if (scmi_info->irq)
> > >    wait_for_completion(&scmi_info->tx_complete);
> > >    scmi_rx_callback(scmi_info->cinfo, shmem_read_header(scmi_info->shmem));
> > >    mutex_unlock(&scmi_info->shmem_lock);
> > >    /* Only SMCCC_RET_NOT_SUPPORTED is valid error code */
> > >    if (res.a0)
> > >    return -EOPNOTSUPP;
> > >    return 0;
> > >  }
> > >  #define EOPNOTSUPP 95 /* Operation not supported on transport endpoint */
> > >  I also check the code where Unhandled SMC/HVC print in xen,
> > >  and found the log cause by unhandled SMCCC call in function vsmccc_handle_call().
> > >  Could it be xen unhandle SMCCC call cause SCMI driver probe failed ?
> >  Yes. The domain would need to talk to the host SCMI. This is not yet 
> >  supported because Xen doesn't provide a mediator (this is necessary to 
> >  ensure the safety of the call).
> >  If you are *only* looking to use the Mali driver in dom0. So you could 
> >  add some code in Xen to forward simply forward the request to the host 
> >  and check if it helps you.
> How can I pass the requset to the host? I'm not familiar with xen code, 
> is there any
> reference code in xen?
There are a couple of solution:
  1) You request the hypervisor to avoid trapping SVC. This would also 
need some changes in Linux to force the Mali driver to use SVC rather 
than HVC. There is a patch on xen-devel, to avoid trapping (see [1]).
  2) Add an allow list of the SMCCC operations. There are some examples 
how to "emulate" SMC call in Xen (see vsmccc_handle_call()).
Cheers,

[1] 
https://lore.kernel.org/xen-devel/alpine.DEB.2.21.2106241749310.24906@sstabellini-ThinkPad-T480s/
> Best regards
> Cailigang
--
Julien Grall