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[209.132.180.67]) by mx.google.com with ESMTP id ay4-v6si18058508plb.410.2018.11.12.09.47.05; Mon, 12 Nov 2018 09:47:21 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730106AbeKMDjg (ORCPT + 99 others); Mon, 12 Nov 2018 22:39:36 -0500 Received: from mail.bootlin.com ([62.4.15.54]:54402 "EHLO mail.bootlin.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727185AbeKMDjg (ORCPT ); Mon, 12 Nov 2018 22:39:36 -0500 Received: by mail.bootlin.com (Postfix, from userid 110) id 66916208A0; Mon, 12 Nov 2018 18:45:19 +0100 (CET) X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on mail.bootlin.com X-Spam-Level: X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED,SHORTCIRCUIT, URIBL_BLOCKED shortcircuit=ham autolearn=disabled version=3.4.2 Received: from bbrezillon (91-160-177-164.subs.proxad.net [91.160.177.164]) by mail.bootlin.com (Postfix) with ESMTPSA id CBAD4206D8; Mon, 12 Nov 2018 18:45:18 +0100 (CET) Date: Mon, 12 Nov 2018 18:45:18 +0100 From: Boris Brezillon To: Miquel Raynal Cc: Liang Yang , Rob Herring , Hanjie Lin , Victor Wan , Jianxin Pan , Neil Armstrong , Martin Blumenstingl , Richard Weinberger , Yixun Lan , linux-kernel@vger.kernel.org, Marek Vasut , Jian Hu , linux-mtd@lists.infradead.org, Kevin Hilman , Carlo Caione , linux-amlogic@lists.infradead.org, Brian Norris , David Woodhouse , linux-arm-kernel@lists.infradead.org, Jerome Brunet , Wolfram Sang Subject: Re: [PATCH v6 2/2] mtd: rawnand: meson: add support for Amlogic NAND flash controller Message-ID: <20181112184518.6c02ac6d@bbrezillon> In-Reply-To: <20181112175416.247e3203@bbrezillon> References: <1541090542-19618-1-git-send-email-jianxin.pan@amlogic.com> <1541090542-19618-3-git-send-email-jianxin.pan@amlogic.com> <20181105165321.7ea2b45f@bbrezillon> <20181106102851.61deb97a@bbrezillon> <20181106112206.65a70a81@bbrezillon> <20181112171351.4ac3506b@xps13> <20181112175416.247e3203@bbrezillon> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 12 Nov 2018 17:54:16 +0100 Boris Brezillon wrote: > +Wolfram to give some inputs on the DMA issue. > > On Mon, 12 Nov 2018 17:13:51 +0100 > Miquel Raynal wrote: > > > Hello, > > > > Boris Brezillon wrote on Tue, 6 Nov 2018 > > 11:22:06 +0100: > > > > > On Tue, 6 Nov 2018 18:00:37 +0800 > > > Liang Yang wrote: > > > > > > > On 2018/11/6 17:28, Boris Brezillon wrote: > > > > > On Tue, 6 Nov 2018 17:08:00 +0800 > > > > > Liang Yang wrote: > > > > > > > > > >> On 2018/11/5 23:53, Boris Brezillon wrote: > > > > >>> On Fri, 2 Nov 2018 00:42:21 +0800 > > > > >>> Jianxin Pan wrote: > > > > >>> > > > > >>>> + > > > > >>>> +static inline u8 meson_nfc_read_byte(struct mtd_info *mtd) > > > > >>>> +{ > > > > >>>> + struct nand_chip *nand = mtd_to_nand(mtd); > > > > >>>> + struct meson_nfc *nfc = nand_get_controller_data(nand); > > > > >>>> + u32 cmd; > > > > >>>> + > > > > >>>> + cmd = nfc->param.chip_select | NFC_CMD_DRD | 0; > > > > >>>> + writel(cmd, nfc->reg_base + NFC_REG_CMD); > > > > >>>> + > > > > >>>> + meson_nfc_drain_cmd(nfc); > > > > >>> > > > > >>> You probably don't want to drain the FIFO every time you read a byte on > > > > >>> the bus, and I guess the INPUT FIFO is at least as big as the CMD > > > > >>> FIFO, right? If that's the case, you should queue as much DRD cmd as > > > > >>> possible and only sync when the user explicitly requests it or when > > > > >>> the INPUT/READ FIFO is full. > > > > >>> > > > > >> Register 'NFC_REG_BUF' can holds only 4 bytes, also DRD sends only one > > > > >> nand cycle to read one byte and covers the 1st byte every time reading. > > > > >> i think nfc controller is faster than nand cycle, but really it is not > > > > >> high efficiency when reading so many bytes once. > > > > >> Or use dma command here like read_page and read_page_raw. > > > > > > > > > > Yep, that's also an alternative, though you'll have to make sure the > > > > > buffer passed through the nand_op_inst is DMA-safe, and use a bounce > > > > > buffer when that's not the case. > > > > > > > > > ok, i will try dma here. > > > > > > We should probably expose the bounce buf handling as generic helpers at > > > the rawnand level: > > > > > > void *nand_op_get_dma_safe_input_buf(struct nand_op_instr *instr) > > > { > > > void *buf; > > > > > > if (WARN_ON(instr->type != NAND_OP_DATA_IN_INSTR)) > > > return NULL; > > > > > > if (virt_addr_valid(instr->data.in) && > > > !object_is_on_stack(instr->data.buf.in)) > > > return instr->data.buf.in; > > > > > > return kzalloc(instr->data.len, GFP_KERNEL); > > > } > > > > > > void nand_op_put_dma_safe_input_buf(struct nand_op_instr *instr, > > > void *buf) > > > { > > > if (WARN_ON(instr->type != NAND_OP_DATA_IN_INSTR) || > > > WARN_ON(!buf)) > > > return; > > > > > > if (buf == instr->data.buf.in) > > > return; > > > > > > memcpy(instr->data.buf.in, buf, instr->data.len); > > > kfree(buf); > > > } > > > > > > const void *nand_op_get_dma_safe_output_buf(struct nand_op_instr *instr) > > > { > > > void *buf; > > > > > > if (WARN_ON(instr->type != NAND_OP_DATA_OUT_INSTR)) > > > return NULL; > > > > > > if (virt_addr_valid(instr->data.out) && > > > !object_is_on_stack(instr->data.buf.out)) > > > return instr->data.buf.out; > > > > > > return kmemdup(instr->data.buf.out, GFP_KERNEL); > > > } > > > > > > void nand_op_put_dma_safe_output_buf(struct nand_op_instr *instr, > > > void *buf) > > > { > > > if (WARN_ON(instr->type != NAND_OP_DATA_OUT_INSTR) || > > > WARN_ON(!buf)) > > > return; > > > > > > if (buf != instr->data.buf.out) > > > kfree(buf); > > > } > > > > Not that I am against such function, but maybe they should come with > > comments stating that there is no reliable way to find if a buffer is > > DMA-able at runtime and these are just sanity checks (ie. required, but > > probably not enough). > > It's not 100% reliable, but it should cover most cases. Note that the > NAND framework already uses virt_addr_valid() to decide when to use its > internal bounce buffer, so this should be fixed too if we want a fully > reliable solution. > > > This is my understanding of Wolfram's recent talk > > at ELCE [1]. > > Yes, you're right, but the NAND framework does not provide any guarantee > on the buf passed to ->exec_op() simply because the MTD layer does not > provide such a guarantee. Reworking that to match how the i2c framework > handles it is possible (with a flag set when the buffer is known to be > DMA-safe), but it requires rewriting all MTD users if we want to keep > decent perfs (the amount of data transfered to a flash is an order of > magnitude bigger than what you usually receive/send from/to an I2C > device). Also, I'm not even sure the DMA_SAFE flag covers all weird > cases like the "DMA engine embedded in the controller is not able to > access the whole physical memory range" one. I forgot that this problem was handled at dma_map time (a bounce buffer is allocated if needed, and this decision is based on dev->dma_mask). > So ideally we should have > something that checks if a pointer is DMA-safe at the device level and > then at the arch level. > > A temporary solution would be to add a hook at the nand_controller > level: > > bool (*buf_is_dma_safe)(struct nand_chip *chip, void *buf, > size_t len); > > And then fallback to the default implementation when it's not > implemented: > > static bool nand_buf_is_dma_safe(struct nand_chip *chip, void *buf, > size_t len) > { > if (chip->controller->ops && chip->controller->ops->is_dma_safe) > return chip->controller->ops->is_dma_safe(chip, buf, > len); > > return virt_addr_valid(buf) && !object_is_on_stack(buf); > } > > > I suppose using the CONFIG_DMA_API_DEBUG option could help > > more reliably to find such issues. > > Actually, the problem is not only about detecting offenders but being > able to detect when a buffer is not DMA-safe at runtime in order to > allocate/use a bounce buffer.