On Tue, 2009-02-24 at 00:17 +0100, Sebastian Andrzej Siewior wrote: > * Catalin Marinas | 2009-02-17 13:33:53 [+0000]: > > >In the ISP1761 manual, there are some timing diagrams for register > >access. If I understand them correctly (as a software person), there is > >something like minimum 86ns between the end of the write pulse to the > >beginning of the read one. [...] > I would like to NAK this but I don't have a better idea for a proper > fix. > > According to section 14.1.3, table 95 write - read delay is 195ns for > EHCI op regs and the SKIPMAP register is one of those see table 8 in > section 8. So the required delay should be 195ns. My datasheet for ISP1760 doesn't have a table 95 in section 14.1.3 (but in the next section). However the ISP1761 data sheet has a section 15.1.1.3 mentioning the 195ns delay for the EHCI registers. > So after long thinking I'm fine with this patch. Please update your > comment and add _why_ this delay is required. That's an updated patch: Add a delay before reading the SKIPMAP registers in isp1760-hcd.c From: Catalin Marinas <catalin.marinas@xxxxxxx> The data read from the SKIPMAP registers is not immediately available after writing and the driver panics when a packet is enqueued from the interrupt handler. This patch adds an ndelay(195) before these registers are read (delay value mentioned in section 15.1.1.3 of the ISP1760 data sheet). Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx> --- drivers/usb/host/isp1760-hcd.c | 14 ++++++++++++++ 1 files changed, 14 insertions(+), 0 deletions(-) diff --git a/drivers/usb/host/isp1760-hcd.c b/drivers/usb/host/isp1760-hcd.c index 8ee2f41..8d57182 100644 --- a/drivers/usb/host/isp1760-hcd.c +++ b/drivers/usb/host/isp1760-hcd.c @@ -819,6 +819,13 @@ static void enqueue_an_ATL_packet(struct usb_hcd *hcd, struct isp1760_qh *qh, u32 atl_regs, payload; u32 buffstatus; + /* + * When this function is called from the interrupt handler to enqueue + * a follow-up packet, the SKIP register gets written and read back + * almost immediately. With ISP1761, this register requires a delay of + * 195ns between a write and subsequent read (see section 15.1.1.3). + */ + ndelay(195); skip_map = isp1760_readl(hcd->regs + HC_ATL_PTD_SKIPMAP_REG); BUG_ON(!skip_map); @@ -853,6 +860,13 @@ static void enqueue_an_INT_packet(struct usb_hcd *hcd, struct isp1760_qh *qh, u32 int_regs, payload; u32 buffstatus; + /* + * When this function is called from the interrupt handler to enqueue + * a follow-up packet, the SKIP register gets written and read back + * almost immediately. With ISP1761, this register requires a delay of + * 195ns between a write and subsequent read (see section 15.1.1.3). + */ + ndelay(195); skip_map = isp1760_readl(hcd->regs + HC_INT_PTD_SKIPMAP_REG); BUG_ON(!skip_map); Thanks. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
