Re: [RFC] usb: host: xhci-mem: Write high first on erst base of secondary interrupter

[Jung Daehwan]

On Wed, May 22, 2024 at 04:40:56PM +0300, Mathias Nyman wrote:
> On 22.5.2024 4.03, Daehwan Jung wrote:
> >ERSTBA_HI should be written first on secondary interrupter.
> >That's why secondary interrupter could be set while Host Controller
> >is already running.
> >
> >[Synopsys]- The host controller was design to support ERST setting
> >during the RUN state. But since there is a limitation in controller
> >in supporting separate ERSTBA_HI and ERSTBA_LO programming,
> >It is supported when the ERSTBA is programmed in 64bit,
> >or in 32 bit mode ERSTBA_HI before ERSTBA_LO
> 
> xHCI specification 5.1 "Register Conventions "states that 64 bit
> registers should be written in low-high order
> 
> >
> >[Synopsys]- The internal initialization of event ring fetches
> >the "Event Ring Segment Table Entry" based on the indication of
> >ERSTBA_LO written.
> >
> 
> Any idea if this is a common issue with this host?
> Should other 64 bit registers also be written in reverse order.
> 
> >Signed-off-by: Daehwan Jung <dh10.jung@xxxxxxxxxxx>
> >---
> >  drivers/usb/host/xhci-mem.c | 5 ++++-
> >  drivers/usb/host/xhci.h     | 6 ++++++
> >  2 files changed, 10 insertions(+), 1 deletion(-)
> >
> >diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> >index 3100219..36ee704 100644
> >--- a/drivers/usb/host/xhci-mem.c
> >+++ b/drivers/usb/host/xhci-mem.c
> >@@ -2325,7 +2325,10 @@ xhci_add_interrupter(struct xhci_hcd *xhci, struct xhci_interrupter *ir,
> >  	erst_base = xhci_read_64(xhci, &ir->ir_set->erst_base);
> >  	erst_base &= ERST_BASE_RSVDP;
> >  	erst_base |= ir->erst.erst_dma_addr & ~ERST_BASE_RSVDP;
> >-	xhci_write_64(xhci, erst_base, &ir->ir_set->erst_base);
> >+	if (intr_num == 0)
> >+		xhci_write_64(xhci, erst_base, &ir->ir_set->erst_base);
> >+	else
> >+		xhci_write_64_r(xhci, erst_base, &ir->ir_set->erst_base);
> 
> This may cause issues with other hosts expecting low-high order as stated
> in the specification.
> 
> If all 64 bit registers should be written in high-low order for this host then
> maybe set a quirk flag and change xhci_write_64()instead.
> 
> xhci_write_64(...)
> {
> 	if (xhci->quirks & XHCI_WRITE_64_HI_LO)
> 		hi_lo_writeq(val, regs);
> 	else
> 		lo_hi_writeq(val, regs);
> }
> 

Mathias, Thanks for the comment.

I've seen this issue only writing the base address of ERST.
It's better to use a quirk flag as you said.
How about using the quirk only in xhci_add_interrupter?

@@ -2325,7 +2325,10 @@ xhci_add_interrupter(struct xhci_hcd *xhci, struct xhci_interrupter *ir,
  	erst_base = xhci_read_64(xhci, &ir->ir_set->erst_base);
  	erst_base &= ERST_BASE_RSVDP;
  	erst_base |= ir->erst.erst_dma_addr & ~ERST_BASE_RSVDP;
	xhci_write_64(xhci, erst_base, &ir->ir_set->erst_base);
 	if (xhci->quirks & XHCI_WRITE_64_HI_LO)
		xhci_write_64_r(xhci, erst_base, &ir->ir_set->erst_base);
	else
		xhci_write_64(xhci, erst_base, &ir->ir_set->erst_base);

OR

@@ -2325,7 +2325,10 @@ xhci_add_interrupter(struct xhci_hcd *xhci, struct xhci_interrupter *ir,
  	erst_base = xhci_read_64(xhci, &ir->ir_set->erst_base);
  	erst_base &= ERST_BASE_RSVDP;
  	erst_base |= ir->erst.erst_dma_addr & ~ERST_BASE_RSVDP;
	xhci_write_64(xhci, erst_base, &ir->ir_set->erst_base);
 	if (!xhci->quirks & XHCI_WRITE_64_HI_LO)
		xhci_write_64(xhci, erst_base, &ir->ir_set->erst_base);
	else
		xhci_write_64_r(xhci, erst_base, &ir->ir_set->erst_base);

}

> Thanks
> Mathias
>