From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B8531C43143 for ; Tue, 2 Oct 2018 13:19:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5D53E206B2 for ; Tue, 2 Oct 2018 13:19:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5D53E206B2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ACULAB.COM Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726721AbeJBUC2 convert rfc822-to-8bit (ORCPT ); Tue, 2 Oct 2018 16:02:28 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([146.101.78.151]:47586 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726293AbeJBUC2 (ORCPT ); Tue, 2 Oct 2018 16:02:28 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by eu-smtp-1.mimecast.com with ESMTP id uk-mta-113-64szs7q2PG2j0IWq2mX6bQ-1; Tue, 02 Oct 2018 14:19:07 +0100 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Tue, 2 Oct 2018 14:19:07 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Tue, 2 Oct 2018 14:19:07 +0100 From: David Laight To: 'Ben Dooks' , "netdev@vger.kernel.org" CC: "oneukum@suse.com" , "davem@davemloft.net" , "linux-usb@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-kernel@lists.codethink.co.uk" Subject: RE: [PATCH 2/4] usbnet: smsc95xx: align tx-buffer to word Thread-Topic: [PATCH 2/4] usbnet: smsc95xx: align tx-buffer to word Thread-Index: AQHUWjIR+wUuyITS3UylBDg14qAu6qUL7Sug Date: Tue, 2 Oct 2018 13:19:07 +0000 Message-ID: <59988ed22559410881addfecf58335eb@AcuMS.aculab.com> References: <20181002092645.1115-1-ben.dooks@codethink.co.uk> <20181002092645.1115-3-ben.dooks@codethink.co.uk> In-Reply-To: <20181002092645.1115-3-ben.dooks@codethink.co.uk> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-MC-Unique: 64szs7q2PG2j0IWq2mX6bQ-1 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Ben Dooks > Sent: 02 October 2018 10:27 > > The tegra driver requires alignment of the buffer, so try and > make this better by pushing the buffer start back to an word > aligned address. At the worst this makes memcpy() easier as > it is word aligned, at best it makes sure the usb can directly > map the buffer. > > Signed-off-by: Ben Dooks > [todo - make this configurable] > --- > drivers/net/usb/Kconfig | 12 ++++++++++++ > drivers/net/usb/smsc95xx.c | 22 ++++++++++++++++++++-- > 2 files changed, 32 insertions(+), 2 deletions(-) > > diff --git a/drivers/net/usb/Kconfig b/drivers/net/usb/Kconfig ... > +static bool align_tx = IS_ENABLED(CONFIG_USB_NET_SMSC95XX_TXALIGN); > +module_param(align_tx, bool, 0644); > +MODULE_PARM_DESC(align_tx, "Align TX buffers to word boundaries"); DM doesn't like module parameters. > static bool turbo_mode = IS_ENABLED(CONFIG_USB_NET_SMSC95XX_TURBO); > module_param(turbo_mode, bool, 0644); > MODULE_PARM_DESC(turbo_mode, "Enable multiple frames per Rx transaction"); > @@ -2005,10 +2009,18 @@ static struct sk_buff *smsc95xx_tx_fixup(struct usbnet *dev, > bool csum = skb->ip_summed == CHECKSUM_PARTIAL; > int overhead = csum ? SMSC95XX_TX_OVERHEAD_CSUM : SMSC95XX_TX_OVERHEAD; > u32 tx_cmd_a, tx_cmd_b; > + u32 data_len; > + uintptr_t align = 0; > > /* We do not advertise SG, so skbs should be already linearized */ > BUG_ON(skb_shinfo(skb)->nr_frags); > > + if (IS_ENABLED(CONFIG_USB_NET_SMSC95XX_TXALIGN) && align_tx) { > + align = (uintptr_t)skb->data & 3; > + if (align) > + overhead += 4 - align; Better to calculate the pad size once: align = (-(long)skb->data) & 3; should do it - and you can unconditionally add it in. > + } > + > /* Make writable and expand header space by overhead if required */ > if (skb_cow_head(skb, overhead)) { > /* Must deallocate here as returning NULL to indicate error > @@ -2037,16 +2049,22 @@ static struct sk_buff *smsc95xx_tx_fixup(struct usbnet *dev, > } > } > > + data_len = skb->len; > + if (align) > + skb_push(skb, 4 - align); > + > skb_push(skb, 4); You don't want to call skb_push() twice. IIRC really horrid things happen if the data has to be copied. (Actually what happens to the alignment in that case??) And there is another skb_push() below.... > - tx_cmd_b = (u32)(skb->len - 4); > + tx_cmd_b = (u32)(data_len); You don't need the cast here at all (if it was ever needed). Actually you don't need the new 'data_len' variable. Just set tx_cmd_b earlier. ... David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)