Received-SPF: pass (google.com: best guess record for domain of linux-wireless-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 12 Jun 2019 13:17:27 +0200
From:   Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
To:     Stanislaw Gruszka <sgruszka@redhat.com>
Cc:     Lorenzo Bianconi <lorenzo@kernel.org>, nbd@nbd.name,
        kvalo@codeaurora.org, linux-wireless@vger.kernel.org
Subject: Re: [PATCH v2 1/2] mt76: usb: fix rx A-MSDU support
Message-ID: <20190612111726.GG8107@localhost.localdomain>
References: <cover.1559293385.git.lorenzo@kernel.org>
 <52ea155d9889aa15df44b4910806b74fa2fd9056.1559293385.git.lorenzo@kernel.org>
 <20190612085844.GA2965@redhat.com>
 <20190612094519.GC8107@localhost.localdomain>
 <20190612100014.GA4431@redhat.com>
 <20190612102133.GE8107@localhost.localdomain>
 <20190612105801.GA2600@redhat.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;
        protocol="application/pgp-signature"; boundary="8S1fMsFYqgBC+BN/"
Content-Disposition: inline
In-Reply-To: <20190612105801.GA2600@redhat.com>
User-Agent: Mutt/1.11.4 (2019-03-13)
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk


--8S1fMsFYqgBC+BN/
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

> On Wed, Jun 12, 2019 at 12:21:34PM +0200, Lorenzo Bianconi wrote:
> > On Jun 12, Stanislaw Gruszka wrote:
> > > On Wed, Jun 12, 2019 at 11:45:21AM +0200, Lorenzo Bianconi wrote:
> > > > > > +mt76u_build_rx_skb(u8 *data, int len, int buf_size,
> > > > > > +		   int *nsgs)
> > > > > > +{
> > > > > > +	int data_len =3D min(len, MT_SKB_HEAD_LEN);
> > >=20
> > > Oh, and this looks unneeded as well as for len < MT_SKB_HEAD_LEN=3D128
> > > we will go through fast path.
> >=20
> > I guess if we remove data_len =3D min(len, MT_SKB_HEAD_LEN) and even *n=
sgs =3D 0 at
> > the end we are making some assumptions on the value of MT_SKB_HEAD_LEN =
and
> > buf_size. In the patch I just avoided them but maybe we can just assume=
 that
> > MT_SKB_HEAD_LEN and buf_size will not changed in the future. What do you
> > think?
>=20
> Yes, sure. Other drivers just use 128 value directly and don't even
> create a macro for that. And if somebody will decide to change
> buf_size it will not be small value.

Ok, I will simplify it in v2

>=20
> > > > > mt7601u and iwlmvm just copy hdrlen + 8 and put the rest
> > > > > of the buffer in fragment, which supose to be more efficient,
> > > > > see comment in iwl_mvm_pass_packet_to_mac80211().
> > > >=20
> > > > Right here we copy 128B instead of 32 but I think it is good to hav=
e L3 and L4
> > > > header in the linear area of the skb since otherwise the stack will=
 need to
> > > > align them
> > >=20
> > > Not sure if understand, I think aliment of L3 & L4 headers will be
> > > the same, assuming ieee80211 header is aligned the same in fragment
> > > buffer and in linear area. But if you think this is better to copy th=
ose
> > > to linear area I'm ok with that.
> >=20
> > Sorry I have not been so clear. I mean in the stack before accessing a =
given
> > header we will run pskb_may_pull() that can end up copying the skb if t=
here is
> > not enough space in the skb->head
>=20
> Ok, so L3 and L4 headers should be in linear area of skb and if not=20
> network stack will copy them from fragment. But I wonder why other
> drivers just copy ieee80211_hdr and SNAP ? Isn't that if we copy=20
> 128B then is possible that part of the payload will be in linear
> area and part in fragment, whereas is expected that payload
> will not be broken into two parts?

I think the payload can be split in multiple skb fragments, the constraint =
is
just related to header parsing

Regards,
Lorenzo


>=20
> Stanislaw

--8S1fMsFYqgBC+BN/
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iHUEABYIAB0WIQTquNwa3Txd3rGGn7Y6cBh0uS2trAUCXQDfQwAKCRA6cBh0uS2t
rDDtAP491tp1JlE/akouftzGYRMlKSFeVSnWrNE/liO3+QT1fQEA49O/6PzYH2w2
hRNTIaoDE/4Bp8Y9iIYs8X/Acw4Ubwk=
=ROjx
-----END PGP SIGNATURE-----

--8S1fMsFYqgBC+BN/--