Date: Wed, 11 Dec 2013 11:56:22 +0100 From: Hans Petter Selasky <hps@bitfrost.no> To: Kohji Okuno <okuno.kohji@jp.panasonic.com>, freebsd-current@FreeBSD.org, freebsd-usb@freebsd.org Subject: Re: spec violation of xHCI? Message-ID: <52A844D6.7050203@bitfrost.no> In-Reply-To: <20131211.191212.1888965979017331164.okuno.kohji@jp.panasonic.com> References: <20131211.191212.1888965979017331164.okuno.kohji@jp.panasonic.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On 12/11/13 11:12, Kohji Okuno wrote:
> Hi,
>
> I think the xHCI host controller driver has a spec violation.
>
> Could you refer to
> ``Table 126: Offset 0Ch – Link TRB Field Definitions''
> in xHCI_Specification_for_USB.pdf(Revision 1.0)?
>
> The following is an excerpt about the CHAIN BIT.
>
> Chain bit (CH). Set to ‘1’ by software to associate this TRB with
> the next TRB on the Ring. A Transfer Descriptor (TD) is defined as
> one or more TRBs. The Chain bit is used to identify the TRBs that
> comprise a TD. Refer to section 4.11.7 for more information on Link
> TRB placement within a TD. On a Command Ring this bit is ignored by
> the xHC.
>
>
> I think that we should add XHCI_TRB_3_CHAIN_BIT to line 1895.
> How do you think?
>
Hi Kohji,
The double word written at line 1895 does not set the "chain bit"
because this is the end of a transfer descriptor, TD. I'm unsure how
hardware interprets this bit, if setting the bit on the previous TRB
makes the next one connect to the previous one, or the other way around.
If setting this bit makes the TRB connect to the previous one, you are
correct. Else the current code is correct.
Thank you!
--HPS
>
> src/sys/dev/usb/controller/xhci.c:
> 1879 /* fill out link TRB */
> 1880
> 1881 if (td_next != NULL) {
> 1882 /* link the current TD with the next one */
> 1883 td->td_trb[x].qwTrb0 = htole64((uint64_t)td_next->td_self);
> 1884 DPRINTF("LINK=0x%08llx\n", (long long)td_next->td_self);
> 1885 } else {
> 1886 /* this field will get updated later */
> 1887 DPRINTF("NOLINK\n");
> 1888 }
> 1889
> 1890 dword = XHCI_TRB_2_IRQ_SET(0);
> 1891
> 1892 td->td_trb[x].dwTrb2 = htole32(dword);
> 1893
> 1894 dword = XHCI_TRB_3_TYPE_SET(XHCI_TRB_TYPE_LINK) |
> 1895 XHCI_TRB_3_CYCLE_BIT | XHCI_TRB_3_IOC_BIT;
> 1896
> 1897 td->td_trb[x].dwTrb3 = htole32(dword);
> 1898
> 1899 td->alt_next = td_alt_next;
>
> --
> Best regards,
> Kohji Okuno
>
> _______________________________________________
> freebsd-usb@freebsd.org mailing list
> http://lists.freebsd.org/mailman/listinfo/freebsd-usb
> To unsubscribe, send any mail to "freebsd-usb-unsubscribe@freebsd.org"
>
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?52A844D6.7050203>