linux-kernel - Re: [linux-nfc] [PATCH 1/8] NFC: NCI: Allow connection close with dev down

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Message-ID: <20150524170747.GB15886@ribalta.ccr.corp.intel.com>
Date:	Sun, 24 May 2015 19:07:47 +0200
From:	Samuel Ortiz <sameo@...ux.intel.com>
To:	Robert Dolca <robert.dolca@...il.com>
Cc:	Robert Dolca <robert.dolca@...el.com>, linux-nfc@...ts.01.org,
	netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [linux-nfc] [PATCH 1/8] NFC: NCI: Allow connection close with
 dev down

Hi Robert,

On Tue, Mar 31, 2015 at 05:03:42PM +0300, Robert Dolca wrote:
> On Thu, Mar 26, 2015 at 2:29 AM, Samuel Ortiz <sameo@...ux.intel.com> wrote:
> > Hi Robert,
> >
> > On Tue, Feb 24, 2015 at 12:01:45PM +0200, Robert Dolca wrote:
> >> By calling __nci_request instead of nci_request allows the driver to use
> >> the function while initializing the device (setup stage)
> >>
> >> Signed-off-by: Robert Dolca <robert.dolca@...el.com>
> >> ---
> >>  net/nfc/nci/core.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c
> >> index 9575a18..c4dd5d8 100644
> >> --- a/net/nfc/nci/core.c
> >> +++ b/net/nfc/nci/core.c
> >> @@ -558,7 +558,7 @@ static void nci_core_conn_close_req(struct nci_dev *ndev, unsigned long opt)
> >>
> >>  int nci_core_conn_close(struct nci_dev *ndev, u8 conn_id)
> >>  {
> >> -     return nci_request(ndev, nci_core_conn_close_req, conn_id,
> >> +     return __nci_request(ndev, nci_core_conn_close_req, conn_id,
> >>                               msecs_to_jiffies(NCI_CMD_TIMEOUT));
> > You're fixing your problem by removing the NCI request serialization and
> > removing the check for your device being UP.
> > I assume you need to open and close a proprietary connection from your
> > setup hook ? Then please extend nci_request() to check for both NCI_UP
> > and NCI_INIT.
> 
> You are right, I am opening and closing a connection from the setup
> function. The setup is called by nci_open_device. At the beginning of
> nci_open_device, req_lock is being acquired and it is release at the
> end of the function. That means that when setup is being called
> req_lock is acuired. As you said I can modify nci_request to check for
> NCI_INIT but it tries to acquire req_lock and it can not succeed.
I see, I thought the issue was only about checking the NCI_* flags.

As a short term solution, I propose you do the following:

a) Export nci_core_conn_create_req, nci_core_conn_close_req and
__nci_request.
b) Call __nci_request() directly from your fdp_nci_close_conn() and
fdp_nci_create_conn() routines.

The long term, scalable fix would be to implement and export an
__nci_send_cmd_sync() routine, that would transparently build an NCI
request and tail it to the ndev req skb queue, and put the caller on a
wait queue. The created request's response callback would then wake the
caller up.

Cheers,
Samuel.
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