From: Liang Yang <liang.yang@amlogic.com>
To: Boris Brezillon <boris.brezillon@bootlin.com>,
Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Rob Herring <robh@kernel.org>,
Hanjie Lin <hanjie.lin@amlogic.com>,
Victor Wan <victor.wan@amlogic.com>,
Jianxin Pan <jianxin.pan@amlogic.com>,
Neil Armstrong <narmstrong@baylibre.com>,
Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
Richard Weinberger <richard@nod.at>,
Yixun Lan <yixun.lan@amlogic.com>, <linux-kernel@vger.kernel.org>,
Marek Vasut <marek.vasut@gmail.com>,
Jian Hu <jian.hu@amlogic.com>, <linux-mtd@lists.infradead.org>,
Kevin Hilman <khilman@baylibre.com>,
Carlo Caione <carlo@caione.org>,
<linux-amlogic@lists.infradead.org>,
Brian Norris <computersforpeace@gmail.com>,
David Woodhouse <dwmw2@infradead.org>,
<linux-arm-kernel@lists.infradead.org>,
Jerome Brunet <jbrunet@baylibre.com>,
Wolfram Sang <wsa@the-dreams.de>
Subject: Re: [PATCH v6 2/2] mtd: rawnand: meson: add support for Amlogic NAND flash controller
Date: Thu, 15 Nov 2018 19:25:07 +0800 [thread overview]
Message-ID: <27769252-ac5e-e787-6792-d6a06e7af0e4@amlogic.com> (raw)
In-Reply-To: <20181112184518.6c02ac6d@bbrezillon>
Hi Boris,
I have implemented dma access base on these helpers you provided below.
we prepare to send v7 version now, so when will these helpers be pushed?
On 2018/11/13 1:45, Boris Brezillon wrote:
> On Mon, 12 Nov 2018 17:54:16 +0100
> Boris Brezillon <boris.brezillon@bootlin.com> wrote:
>
>> +Wolfram to give some inputs on the DMA issue.
>>
>> On Mon, 12 Nov 2018 17:13:51 +0100
>> Miquel Raynal <miquel.raynal@bootlin.com> wrote:
>>
>>> Hello,
>>>
>>> Boris Brezillon <boris.brezillon@bootlin.com> wrote on Tue, 6 Nov 2018
>>> 11:22:06 +0100:
>>>
>>>> On Tue, 6 Nov 2018 18:00:37 +0800
>>>> Liang Yang <liang.yang@amlogic.com> wrote:
>>>>
>>>>> On 2018/11/6 17:28, Boris Brezillon wrote:
>>>>>> On Tue, 6 Nov 2018 17:08:00 +0800
>>>>>> Liang Yang <liang.yang@amlogic.com> wrote:
>>>>>>
>>>>>>> On 2018/11/5 23:53, Boris Brezillon wrote:
>>>>>>>> On Fri, 2 Nov 2018 00:42:21 +0800
>>>>>>>> Jianxin Pan <jianxin.pan@amlogic.com> 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.
>
> .
>
next prev parent reply other threads:[~2018-11-15 11:25 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-01 16:42 [PATCH v6 0/2] mtd: rawnand: meson: add Amlogic NAND driver support Jianxin Pan
2018-11-01 16:42 ` [PATCH v6 1/2] dt-bindings: nand: meson: add Amlogic NAND controller driver Jianxin Pan
2018-11-01 16:42 ` [PATCH v6 2/2] mtd: rawnand: meson: add support for Amlogic NAND flash controller Jianxin Pan
2018-11-05 15:53 ` Boris Brezillon
2018-11-06 9:08 ` Liang Yang
2018-11-06 9:28 ` Boris Brezillon
2018-11-06 10:00 ` Liang Yang
2018-11-06 10:22 ` Boris Brezillon
2018-11-06 11:08 ` Liang Yang
2018-11-06 16:16 ` Boris Brezillon
2018-11-07 2:13 ` Liang Yang
2018-11-08 7:41 ` Liang Yang
2018-11-12 16:13 ` Miquel Raynal
2018-11-12 16:54 ` Boris Brezillon
2018-11-12 17:45 ` Boris Brezillon
2018-11-15 11:25 ` Liang Yang [this message]
2018-11-15 13:04 ` Miquel Raynal
2018-11-15 13:09 ` Boris Brezillon
2018-11-16 8:29 ` Liang Yang
2018-11-11 20:57 ` [PATCH v6 0/2] mtd: rawnand: meson: add Amlogic NAND driver support Miquel Raynal
2018-11-14 6:42 ` Jianxin Pan
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