Low umass performance with USB 2.0 ports

[Eygene A. Ryabinkin]

> Actually, I just peeked inside the Linux EHCI code and it does a dummy
> read immediately after writing to the status register:
> 
>         /* clear (just) interrupts */
>         writel (status, &ehci->regs->status);
>         readl (&ehci->regs->command);   /* unblock posted write */
> 
> I wonder if that's the whole trick here.  Would someone be willing to
> try the attached patch instead of the one that Ian posted?
 Yes, that solved my problem. But the patch (for 5.x) uses different line
numbers:
-----
--- /sys/dev/usb/ehci.c.orig	Thu Sep  1 10:59:51 2005
+++ /sys/dev/usb/ehci.c	Thu Sep  1 10:48:59 2005
@@ -580,6 +580,7 @@
 		return (0);
 
 	EOWRITE4(sc, EHCI_USBSTS, intrs); /* Acknowledge */
+	EOREAD4(sc, EHCI_USBCMD); /* Flush posted writes on PCI */
 	sc->sc_bus.intr_context++;
 	sc->sc_bus.no_intrs++;
 	if (eintrs & EHCI_STS_IAA) {
-----
 Apart from this the patch works: the writing process still spends much time
in the wdrain state, but no stalls occurs.

 Just a remark: my USB 2.0 controller chip is made by NEC, not VIA.

 For a FAT curiosity: FAT 32 gives 700K/sec and FAT 16 -- 3 Mb/sec.
-- 
 rea