diff options
| author | Marek Vasut <marex@denx.de> | 2012-04-09 04:13:00 +0200 |
|---|---|---|
| committer | Marek Vasut <marex@denx.de> | 2012-05-20 08:32:32 +0200 |
| commit | 41b1f0ac2e4c1d54807f90ae9aa2f2fad22a5151 (patch) | |
| tree | 7ac844375545e21181ac4e85dff1ebd838783439 /drivers/usb | |
| parent | b8adb12095814260d2b5edb23663ddf0ab97b877 (diff) | |
USB: Document the QH and qTD antics in EHCI-HCD
The construction of QH and qTD lists in ehci_submit_async() call is cryptic
business, add at least a bit of comments so if someone is reading it, he can at
least reference the intel ehci manual (ehci-r10.pdf).
Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Diffstat (limited to 'drivers/usb')
| -rw-r--r-- | drivers/usb/host/ehci-hcd.c | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c index a04a6c71d1..04300be110 100644 --- a/drivers/usb/host/ehci-hcd.c +++ b/drivers/usb/host/ehci-hcd.c @@ -234,6 +234,16 @@ ehci_submit_async(struct usb_device *dev, unsigned long pipe, void *buffer, toggle = usb_gettoggle(dev, usb_pipeendpoint(pipe), usb_pipeout(pipe)); + /* + * Setup QH (3.6 in ehci-r10.pdf) + * + * qh_link ................. 03-00 H + * qh_endpt1 ............... 07-04 H + * qh_endpt2 ............... 0B-08 H + * - qh_curtd + * qh_overlay.qt_next ...... 13-10 H + * - qh_overlay.qt_altnext + */ qh.qh_link = cpu_to_hc32((uint32_t)&qh_list | QH_LINK_TYPE_QH); c = (usb_pipespeed(pipe) != USB_SPEED_HIGH && usb_pipeendpoint(pipe) == 0) ? 1 : 0; @@ -255,6 +265,15 @@ ehci_submit_async(struct usb_device *dev, unsigned long pipe, void *buffer, tdp = &qh.qh_overlay.qt_next; if (req != NULL) { + /* + * Setup request qTD (3.5 in ehci-r10.pdf) + * + * qt_next ................ 03-00 H + * qt_altnext ............. 07-04 H + * qt_token ............... 0B-08 H + * + * [ buffer, buffer_hi ] loaded with "req". + */ qtd[qtd_counter].qt_next = cpu_to_hc32(QT_NEXT_TERMINATE); qtd[qtd_counter].qt_altnext = cpu_to_hc32(QT_NEXT_TERMINATE); token = (0 << 31) | @@ -265,12 +284,22 @@ ehci_submit_async(struct usb_device *dev, unsigned long pipe, void *buffer, debug("unable construct SETUP td\n"); goto fail; } + /* Update previous qTD! */ *tdp = cpu_to_hc32((uint32_t)&qtd[qtd_counter]); tdp = &qtd[qtd_counter++].qt_next; toggle = 1; } if (length > 0 || req == NULL) { + /* + * Setup request qTD (3.5 in ehci-r10.pdf) + * + * qt_next ................ 03-00 H + * qt_altnext ............. 07-04 H + * qt_token ............... 0B-08 H + * + * [ buffer, buffer_hi ] loaded with "buffer". + */ qtd[qtd_counter].qt_next = cpu_to_hc32(QT_NEXT_TERMINATE); qtd[qtd_counter].qt_altnext = cpu_to_hc32(QT_NEXT_TERMINATE); token = (toggle << 31) | @@ -284,11 +313,19 @@ ehci_submit_async(struct usb_device *dev, unsigned long pipe, void *buffer, debug("unable construct DATA td\n"); goto fail; } + /* Update previous qTD! */ *tdp = cpu_to_hc32((uint32_t)&qtd[qtd_counter]); tdp = &qtd[qtd_counter++].qt_next; } if (req != NULL) { + /* + * Setup request qTD (3.5 in ehci-r10.pdf) + * + * qt_next ................ 03-00 H + * qt_altnext ............. 07-04 H + * qt_token ............... 0B-08 H + */ qtd[qtd_counter].qt_next = cpu_to_hc32(QT_NEXT_TERMINATE); qtd[qtd_counter].qt_altnext = cpu_to_hc32(QT_NEXT_TERMINATE); token = (toggle << 31) | @@ -298,6 +335,7 @@ ehci_submit_async(struct usb_device *dev, unsigned long pipe, void *buffer, (3 << 10) | ((usb_pipein(pipe) ? 0 : 1) << 8) | (0x80 << 0); qtd[qtd_counter].qt_token = cpu_to_hc32(token); + /* Update previous qTD! */ *tdp = cpu_to_hc32((uint32_t)&qtd[qtd_counter]); tdp = &qtd[qtd_counter++].qt_next; } |