From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.free-electrons.com ([62.4.15.54]) by bombadil.infradead.org with esmtp (Exim 4.87 #1 (Red Hat Linux)) id 1cj1LA-0008VP-Rk for linux-mtd@lists.infradead.org; Wed, 01 Mar 2017 10:18:38 +0000 Date: Wed, 1 Mar 2017 11:18:05 +0100 From: Boris Brezillon To: Cyrille Pitchen Cc: Richard Weinberger , Vignesh R , David Woodhouse , Brian Norris , Marek Vasut , , , , Frode Isaksen , Subject: Re: [RFC PATCH 1/2] mtd: spi-nor: Introduce bounce buffer to handle vmalloc'd buffers Message-ID: <20170301111805.0eb23b76@bbrezillon> In-Reply-To: <65b4a156-f2a8-4c5e-4399-2024a147d5ec@atmel.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 1 Mar 2017 11:09:57 +0100 Cyrille Pitchen wrote: > Le 28/02/2017 =C3=A0 22:39, Richard Weinberger a =C3=A9crit : > > Vignesh, > >=20 > > Am 27.02.2017 um 13:08 schrieb Vignesh R: =20 > >> Filesystems like UBIFS may pass vmalloc'd buffers to SPI NOR layer whi= ch > >> 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. Bu= t, > >> its known that this does not work well with VIVT/aliasing cache > >> architectures. > >> This also fails when buffers are addressed using LPAE (buffers in regi= on > >> 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-n= or.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 > >> =20 > >> #include > >> #include > >> @@ -1205,11 +1206,21 @@ static int spi_nor_read(struct mtd_info *mtd, = loff_t from, size_t len, > >> =20 > >> while (len) { > >> loff_t addr =3D from; > >> + bool use_bb =3D false; > >> + u_char *dst_buf =3D buf; > >> + size_t buf_len =3D len; > >> =20 > >> if (nor->flags & SNOR_F_S3AN_ADDR_DEFAULT) > >> addr =3D spi_nor_s3an_addr_convert(nor, addr); > >> =20 > >> - ret =3D nor->read(nor, addr, len, buf); > >> + if (!virt_addr_valid(buf) && nor->bounce_buf) { =20 >=20 > Should we use is_vmalloc_addr() instead of virt_addr_valid() ? >=20 > 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 :))