linux-kernel - Re: [RFC 4/7] Bluetooth: hci_uart: Add support for word alignment

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Message-ID: <20160816075104.blnfshsv7cgcm7gb@earth>
Date:	Tue, 16 Aug 2016 09:51:04 +0200
From:	Sebastian Reichel <sre@...nel.org>
To:	Marcel Holtmann <marcel@...tmann.org>
Cc:	Tony Lindgren <tony@...mide.com>, Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>, Ville Tervo <ville.tervo@....fi>,
	Filip Matijević <filip.matijevic.pz@...il.com>,
	Aaro Koskinen <aaro.koskinen@....fi>,
	Pavel Machek <pavel@....cz>,
	Pali Rohár <pali.rohar@...il.com>,
	ivo.g.dimitrov.75@...il.com, linux-bluetooth@...r.kernel.org,
	linux-serial@...r.kernel.org, linux-omap@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 4/7] Bluetooth: hci_uart: Add support for word alignment

Hi Marcel,

On Tue, Aug 16, 2016 at 09:05:19AM +0200, Marcel Holtmann wrote:
> Hi Sebatian,
> 
> > This will be used by Nokia's H4+ protocol, which
> > adds padding to packets to reach word alignment.
> > ---
> > drivers/bluetooth/hci_h4.c   | 10 ++++++++++
> > drivers/bluetooth/hci_uart.h |  1 +
> > 2 files changed, 11 insertions(+)
> > 
> > diff --git a/drivers/bluetooth/hci_h4.c b/drivers/bluetooth/hci_h4.c
> > index 635597b6e168..a934e4eb692b 100644
> > --- a/drivers/bluetooth/hci_h4.c
> > +++ b/drivers/bluetooth/hci_h4.c
> > @@ -253,11 +253,21 @@ struct sk_buff *h4_recv_buf(struct hci_dev *hdev, struct sk_buff *skb,
> > 			}
> > 
> > 			if (!dlen) {
> > +				if ((&pkts[i])->wordaligned && !(skb->len % 2)) {
> > +					buffer++;
> > +					count--;
> > +				}
> > +
> > 				/* No more data, complete frame */
> > 				(&pkts[i])->recv(hdev, skb);
> > 				skb = NULL;
> > 			}
> > 		} else {
> > +			if ((&pkts[i])->wordaligned && !(skb->len % 2)) {
> > +				buffer++;
> > +				count--;
> > +			}
> > +
> > 			/* Complete frame */
> > 			(&pkts[i])->recv(hdev, skb);
> > 			skb = NULL;
> > diff --git a/drivers/bluetooth/hci_uart.h b/drivers/bluetooth/hci_uart.h
> > index 839bad1d8152..a7d67aec3632 100644
> > --- a/drivers/bluetooth/hci_uart.h
> > +++ b/drivers/bluetooth/hci_uart.h
> > @@ -121,6 +121,7 @@ struct h4_recv_pkt {
> > 	u8  loff;	/* Data length offset in header */
> > 	u8  lsize;	/* Data length field size */
> > 	u16 maxlen;	/* Max overall packet length */
> > +	bool wordaligned;	/* packets are word aligned */
> 
> I wonder if not a u8 align would be a way better choice here. We
> set it to 1 for all existing packet types. And the Nokia driver
> can use 2 here.

Sounds less hacky than my approach. Also it made me notice, that my
code is not safe, since the buffer size is not checked. I will use
u8 align and fix the buffer size check.

-- Sebastian

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