linux-kernel - Re: [PATCH v7 07/10] usb: dbc: handle endpoint stall

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Date:	Wed, 02 Mar 2016 14:58:59 +0200
From:	Felipe Balbi <balbi@...nel.org>
To:	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Lu Baolu <baolu.lu@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 07/10] usb: dbc: handle endpoint stall


Hi,

Mathias Nyman <mathias.nyman@...ux.intel.com> writes:
> [ text/plain ]
> On 26.01.2016 14:58, Lu Baolu wrote:
>> In case of endpoint stall, software is able to detect the situation
>> by reading DCCTRL.HIT or DCCTRL.HOT bits. DbC follows the normal USB
>> framework to handle endpoint stall. When software detects endpoint
>> stall situation, it should wait until endpoint is recovered before
>> read or write oprations.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> ---
>>   drivers/usb/early/xhci-dbc.c | 36 ++++++++++++++++++++++++++++++++++++
>>   1 file changed, 36 insertions(+)
>>
>> diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
>> index c81df40..344d93e 100644
>> --- a/drivers/usb/early/xhci-dbc.c
>> +++ b/drivers/usb/early/xhci-dbc.c
>> @@ -1163,6 +1163,37 @@ static int xdbc_wait_until_dbc_configured(void)
>>   	return -ETIMEDOUT;
>>   }
>>
>> +static int xdbc_wait_until_epstall_cleared(bool read)
>> +{
>> +	int timeout = 0;
>> +
>> +	if (read) {
>> +		do {
>> +			if (!(readl(&xdbcp->xdbc_reg->control) & CTRL_HIT)) {
>> +				xdbcp->in_ep_state = EP_RUNNING;
>> +
>> +				return 0;
>> +			}
>> +
>> +			xdbcp->in_ep_state = EP_HALTED;
>> +			xdbc_udelay(10);
>> +		} while (timeout++ < XDBC_LOOPS);
>> +	} else {
>> +		do {
>> +			if (!(readl(&xdbcp->xdbc_reg->control) & CTRL_HOT)) {
>> +				xdbcp->out_ep_state = EP_RUNNING;
>> +
>> +				return 0;
>> +			}
>> +
>> +			xdbcp->out_ep_state = EP_HALTED;
>> +			xdbc_udelay(10);
>> +		} while (timeout++ < XDBC_LOOPS);
>> +	}
>> +
>> +	return -ETIMEDOUT;
>> +}
>>
>
> how about something like:
>
> enum xdbc_ep_state *ep_state;
> u32 halt_bit;
>
> if (read) {
> 	ep_state = &xdbcp->in_ep_state
> 	halt_bit = CTRL_HIT
> } else {
>   	ep_state = &xdbcp->out_ep_state
> 	halt_bit = CTRL_HOT
> }
> do {
> 	if (!(readl(..) & halt_bit)) {
> 		*ep_state = EP_RUNNING;
> 		return 0;
> 	}
> 	*ep_state = EP_HALTED;
> 	delay()
> } while (..)

I'll agree, this looks better. Might also want to refactor the handshake
loop to its own function:

static int xdbg_ep_state_handshake(enum xdbc_ep_state *ep_state, u32 halt_bit)
{
        do {
		if (!(readl(...) & halt_bit)) {
                	...
                }
                *ep_state = EP_HALTED;
                delay(...);
        } while (...)

>> @@ -1182,6 +1213,11 @@ static int xdbc_bulk_transfer(void *data, int size, int loops, bool read)
>>   		return -EPERM;
>>   	}
>>
>> +	if (xdbc_wait_until_epstall_cleared(read)) {
>> +		xdbc_trace("%s: endpoint not ready\n", __func__);
>> +		return -EPERM;
>
> Is -EPERM appropriate here?
>
> Not sure about what error codes the device side is using, but usually
> HALT is set due to some Data buffer/transmission/TRB error.

EIO perhaps ?

> In this case the failure is that debug host failed to send a
> clearFeature(EP_HALT) request in time.

I haven't read the spec, but does it define a maximum time for this to
happen ?

-- 
balbi

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