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[149.6.153.186]) by smtp.gmail.com with ESMTPSA id y38sm27767008wrd.41.2019.06.12.03.49.24 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Wed, 12 Jun 2019 03:49:24 -0700 (PDT) Date: Wed, 12 Jun 2019 12:49:22 +0200 From: Lorenzo Bianconi To: Stanislaw Gruszka Cc: Lorenzo Bianconi , nbd@nbd.name, kvalo@codeaurora.org, linux-wireless@vger.kernel.org Subject: Re: [PATCH v2 2/2] mt76: usb: do not always copy the first part of received frames Message-ID: <20190612104921.GF8107@localhost.localdomain> References: <2ed0b595a12944a8cfea14e066bcc4fa24f0ba44.1559293385.git.lorenzo@kernel.org> <20190612091036.GB2965@redhat.com> <20190612095302.GD8107@localhost.localdomain> <20190612102502.GB4431@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="8JPrznbw0YAQ/KXy" Content-Disposition: inline In-Reply-To: <20190612102502.GB4431@redhat.com> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org --8JPrznbw0YAQ/KXy Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable > On Wed, Jun 12, 2019 at 11:53:03AM +0200, Lorenzo Bianconi wrote: > > > On Fri, May 31, 2019 at 11:38:23AM +0200, Lorenzo Bianconi wrote: > >=20 > > [...] > >=20 > > > > } > > > > =20 > > > > urb->num_sgs =3D max_t(int, i, urb->num_sgs); > > > > - urb->transfer_buffer_length =3D urb->num_sgs * q->buf_size, > > > > + urb->transfer_buffer_length =3D urb->num_sgs * data_size; > > > > sg_init_marker(urb->sg, urb->num_sgs); > > > > =20 > > > > return i ? : -ENOMEM; > > > > @@ -611,8 +611,12 @@ static int mt76u_alloc_rx(struct mt76_dev *dev) > > > > if (!q->entry) > > > > return -ENOMEM; > > > > =20 > > > > - q->buf_size =3D dev->usb.sg_en ? MT_RX_BUF_SIZE : PAGE_SIZE; > > > > + if (dev->usb.sg_en) > > > > + q->buf_size =3D MT_BUF_WITH_OVERHEAD(MT_RX_BUF_SIZE); > > >=20 > > > I strongly recommend to not doing this. While this should work > > > in theory creating buffer with size of 2k + some bytes might > > > trigger various bugs in dma mapping or other low level code. > >=20 > > even in practice actually :) >=20 > I wouldn't be sure about this. It's not common to have buffers of > such size and crossing pages boundaries. It really can trigger > nasty bugs on various IOMMU drivers. I was just joking, I mean that it worked in the tests I carried out, but I agree it can trigger some issues in buggy IOMMU drivers >=20 > > but we can be more cautious since probably copying > > the first 128B will not make any difference >=20 > Not sure if I understand what you mean. Please correct me if I am wrong but I think max amsdu rx size is 3839B for mt76. For the sg_en case this frame will span over multiple sg buffers since sg buffer size is 2048B (2 sg buffers). Moreover if we do not take into acc= ount skb_shared_info when configuring the sg buffer size we will need to always = copy the first 128B of the first buffer since received len will be set to 2048 a= nd the following if condition will always fail: if (SKB_WITH_OVERHEAD(buf_size) >=3D MT_DMA_HDR_LEN + len) { } >=20 > > > And skb_shered_info is needed only in first buffer IIUC. > > >=20 > > > Also this patch seems to make first patch unnecessary except for > > > non sg_en case (in which I think rx AMSDU is broken anyway), > > > so I would prefer just to apply first patch. > >=20 > > I do not think rx AMSDU is broken for non sg_en case since the max rx v= alue > > allowed should be 3839 IIRC and we alloc one page in this case >=20 > If that's the case we should be fine, but then I do not understand > why we allocate 8*2k buffers for sg_en case, isn't that AP can > sent AMSDU frame 16k big? Sorry I did not get what you mean here, could you please explain? Regards, Lorenzo >=20 > Stanislaw >=20 --8JPrznbw0YAQ/KXy Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQTquNwa3Txd3rGGn7Y6cBh0uS2trAUCXQDYrgAKCRA6cBh0uS2t rOZCAP4xDy4uWnsqvTxCkpOzU+uPWZ99QAiJcnwjNWM+KLdRHgD9EHrvcWkZorpJ fO4e6QPsunawatvMlEAs7yd1Zu82qAs= =mAXI -----END PGP SIGNATURE----- --8JPrznbw0YAQ/KXy--