From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mga14.intel.com ([192.55.52.115]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1g1uHa-0000sF-GZ for linux-mtd@lists.infradead.org; Mon, 17 Sep 2018 14:13:47 +0000 Subject: Re: [PATCH] mtd: devices: m25p80: Make the buffer passed in op is DMA-able To: Boris Brezillon , David Woodhouse , Brian Norris , Marek Vasut , Richard Weinberger , linux-mtd@lists.infradead.org Cc: stable@vger.kernel.org References: <20180917133652.12442-1-boris.brezillon@bootlin.com> From: Jarkko Nikula Message-ID: <239bb1a4-c986-0f5e-61b9-a08f54947bfe@linux.intel.com> Date: Mon, 17 Sep 2018 17:13:32 +0300 MIME-Version: 1.0 In-Reply-To: <20180917133652.12442-1-boris.brezillon@bootlin.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 09/17/2018 04:36 PM, Boris Brezillon wrote: > As documented in spi-mem.h, spi_mem_op->data.buf.{in,out} must be > DMA-able, and commit 4120f8d158ef ("mtd: spi-nor: Use the spi_mem_xx() > API") failed to follow this rule as buffers passed to > ->{read,write}_reg() are usually placed on the stack. > > Fix that by allocating a scratch buffer and copying the data in there > before passing it to the spi-mem layer. > > Fixes: 4120f8d158ef ("mtd: spi-nor: Use the spi_mem_xx() API") > Reported-by: Jarkko Nikula > Cc: > Signed-off-by: Boris Brezillon > --- > Note that the ->{read,write}() path is still buggy since nothing > guarantees that buffers passed by the MTD layer to the SPI NOR layer > are DMA-able, but this is a long-standing issue which we'll have to > address at the spi-nor level (this layer can choose the bounce buffer > size based on nor->page_size). > --- > drivers/mtd/devices/m25p80.c | 24 +++++++++++++++++++++--- > 1 file changed, 21 insertions(+), 3 deletions(-) > > diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c > index cbfafc453274..3b7fafa4bbd6 100644 > --- a/drivers/mtd/devices/m25p80.c > +++ b/drivers/mtd/devices/m25p80.c > @@ -39,14 +39,22 @@ static int m25p80_read_reg(struct spi_nor *nor, u8 code, u8 *val, int len) > struct spi_mem_op op = SPI_MEM_OP(SPI_MEM_OP_CMD(code, 1), > SPI_MEM_OP_NO_ADDR, > SPI_MEM_OP_NO_DUMMY, > - SPI_MEM_OP_DATA_IN(len, val, 1)); > + SPI_MEM_OP_DATA_IN(len, NULL, 1)); > + void *scratchbuf; > int ret; > > + scratchbuf = kmemdup(val, len, GFP_KERNEL); > + if (!scratchbuf) > + return -ENOMEM; > + > + op.data.buf.in = scratchbuf; > ret = spi_mem_exec_op(flash->spimem, &op); > if (ret < 0) > dev_err(&flash->spimem->spi->dev, "error %d reading %x\n", ret, > code); > > + kfree(scratchbuf); > + Actually this makes things even worse: "unrecognized JEDEC id bytes: b1, 74, 01" since we don't copy scratchbuf to original buffer and kmemdup before bus read is needless :-) -- Jarkko