linux-kernel - Re: [PATCH 5/6] USB: gadget: mv_udc: workaroud for missing dTD

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Date:	Tue, 25 Feb 2014 12:19:17 +0800
From:	Peter Chen <peter.chen@...escale.com>
To:	Neil Zhang <zhangwm@...vell.com>
CC:	<balbi@...com>, <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] USB: gadget: mv_udc: workaroud for missing dTD

On Mon, Feb 24, 2014 at 04:03:15PM +0800, Neil Zhang wrote:
> There is an issue with the add dTD tripwire semaphore (ATDTW bit in
> USBCMD register) that can cause the controller to ignore a dTD that is
> added to a primed endpoint. When this happens, the software can read
> the tripwire bit and the status bit at '1' even though the endpoint
> is unprimed.
> 
> After executing a dTD, the device controller endpoint state machine
> executes a final read of the dTD terminate bit to check if the
> application added a dTD to the linked list at the last moment. This read
> is done in the finpkt_read_latest_next_td (44) state. After the read is
> performed, if the terminate bit is still set, the state machine moves to
> unprime the endpoint. The decision to unprime the endpoint is done in
> the checkqh_decision (59) state, based on the value of the terminate bit.
> 
> Before reaching the checkqh_decision state, the state machine traverses
> the writeqhtd_status (57), writeqh_status (56), and release_prime_mask
> (42) states. As shown in the waveform, the ep_addtd_tripwire_clr signal
> is not set to clear the tripwire bit in these states.
> 
> Signed-off-by: Neil Zhang <zhangwm@...vell.com>
> ---
>  drivers/usb/gadget/mv_udc_core.c |   20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/usb/gadget/mv_udc_core.c b/drivers/usb/gadget/mv_udc_core.c
> index a620cff..8df8606 100644
> --- a/drivers/usb/gadget/mv_udc_core.c
> +++ b/drivers/usb/gadget/mv_udc_core.c
> @@ -196,7 +196,27 @@ static int process_ep_req(struct mv_udc *udc, int index,
>  			while (readl(&udc->op_regs->epstatus) & bit_pos)
>  				udelay(1);
>  			break;
> +		} else {
> +			if (!(readl(&udc->op_regs->epstatus) & bit_pos)) {
> +				/* The DMA engine thinks there is no more dTD */
> +				curr_dqh->next_dtd_ptr = curr_dtd->dtd_next
> +					& EP_QUEUE_HEAD_NEXT_POINTER_MASK;
> +
> +				/* clear active and halt bit */
> +				curr_dqh->size_ioc_int_sts &=
> +						~(DTD_STATUS_ACTIVE
> +						| DTD_STATUS_HALTED);
> +
> +				/* Do prime again */
> +				wmb();
> +				writel(bit_pos, &udc->op_regs->epprime);
> +				while (readl(&udc->op_regs->epprime) & bit_pos)
> +					cpu_relax();
> +
> +				break;
> +			}
>  		}
> +
>  		udelay(1);
>  	}
>  

Is it a chipidea IP issue? Any errate number for this issue?
Does we need it for chipidea driver?

-- 

Best Regards,
Peter Chen

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