Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752695AbdCAL14 (ORCPT ); Wed, 1 Mar 2017 06:27:56 -0500 Received: from mail-wr0-f182.google.com ([209.85.128.182]:36361 "EHLO mail-wr0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752652AbdCAL1w (ORCPT ); Wed, 1 Mar 2017 06:27:52 -0500 Subject: Re: [RFC PATCH 1/2] mtd: spi-nor: Introduce bounce buffer to handle vmalloc'd buffers To: Boris Brezillon , Cyrille Pitchen References: <20170227120839.16545-1-vigneshr@ti.com> <20170227120839.16545-2-vigneshr@ti.com> <8e441369-5c15-d711-1789-b55eadf33c8f@nod.at> <65b4a156-f2a8-4c5e-4399-2024a147d5ec@atmel.com> <20170301111805.0eb23b76@bbrezillon> Cc: Richard Weinberger , Vignesh R , David Woodhouse , Brian Norris , Marek Vasut , linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org, linux-spi@vger.kernel.org From: Frode Isaksen Message-ID: <595ab823-cf40-3b27-55ec-3573cecb456b@baylibre.com> Date: Wed, 1 Mar 2017 12:18:30 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <20170301111805.0eb23b76@bbrezillon> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2864 Lines: 72 On 01/03/2017 11:18, Boris Brezillon wrote: > On Wed, 1 Mar 2017 11:09:57 +0100 > Cyrille Pitchen wrote: > >> Le 28/02/2017 à 22:39, Richard Weinberger a écrit : >>> Vignesh, >>> >>> Am 27.02.2017 um 13:08 schrieb Vignesh R: >>>> Filesystems like UBIFS may pass vmalloc'd buffers to SPI NOR layer which >>>> will end up in SPI layer. SPI core does try to handle such buffers (see >>>> spi_map_buf()) by doing vmalloc_to_page() and creating scatterlist. But, >>>> its known that this does not work well with VIVT/aliasing cache >>>> architectures. >>>> This also fails when buffers are addressed using LPAE (buffers in region >>>> higher than 32 bit addressable region), if DMA is 32bit only. >>>> >>>> Introduce bounce buffers support in SPI NOR framework to handle >>>> vmalloc'd buffers. Use a pre-allocated per flash bounce buffer equal to >>>> the sector size of the flash. Flash drivers can enable this feature by >>>> setting SNOR_F_USE_BOUNCE_BUFFER flag. >>>> This would also enable SPI NOR drivers to safely use DMA in their >>>> read/write callbacks. >>>> >>>> Signed-off-by: Vignesh R >>>> --- >>>> drivers/mtd/spi-nor/spi-nor.c | 30 +++++++++++++++++++++++++++--- >>>> include/linux/mtd/spi-nor.h | 4 ++++ >>>> 2 files changed, 31 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c >>>> index 747645c74134..c241fefa5aff 100644 >>>> --- a/drivers/mtd/spi-nor/spi-nor.c >>>> +++ b/drivers/mtd/spi-nor/spi-nor.c >>>> @@ -17,6 +17,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> >>>> #include >>>> #include >>>> @@ -1205,11 +1206,21 @@ static int spi_nor_read(struct mtd_info *mtd, loff_t from, size_t len, >>>> >>>> while (len) { >>>> loff_t addr = from; >>>> + bool use_bb = false; >>>> + u_char *dst_buf = buf; >>>> + size_t buf_len = len; >>>> >>>> if (nor->flags & SNOR_F_S3AN_ADDR_DEFAULT) >>>> addr = spi_nor_s3an_addr_convert(nor, addr); >>>> >>>> - ret = nor->read(nor, addr, len, buf); >>>> + if (!virt_addr_valid(buf) && nor->bounce_buf) { >> Should we use is_vmalloc_addr() instead of virt_addr_valid() ? >> >> I guess virt_addr_valid() returns true even for kmalloc'ed buffers >> however the copy into the bounce buffer should be avoided for kmalloc'ed >> memory. > The test is !virt_addr_valid(), so we won't use the bounce buffer for > kmalloc-ed regions. I don't remember why we use virt_addr_valid() > instead of is_vmalloc_addr() in the NAND framework, but there was a > good reason (virt_addr_valid() is more restrictive, but I don't > remember why it's safer :)) I think virt_addr_valid() picks up both kmap'ed and vmalloc'ed pages as not valid... Frode > > >