On 6/12/18 2:20 PM, Stefan Agner wrote:
> On 12.06.2018 17:24, Jens Axboe wrote:
>> On 6/12/18 3:17 AM, Stefan Agner wrote:
>>> [also added Jens Axboe]
>>>
>>> On 12.06.2018 10:27, Boris Brezillon wrote:
>>>> On Tue, 12 Jun 2018 10:06:42 +0200
>>>> Stefan Agner <stefan@xxxxxxxx> wrote:
>>>>
>>>>> On 12.06.2018 02:03, Dmitry Osipenko wrote:
>>>>>> On Monday, 11 June 2018 23:52:22 MSK Stefan Agner wrote:
>>>>>>> Add support for the NAND flash controller found on NVIDIA
>>>>>>> Tegra 2 SoCs. This implementation does not make use of the
>>>>>>> command queue feature. Regular operations/data transfers are
>>>>>>> done in PIO mode. Page read/writes with hardware ECC make
>>>>>>> use of the DMA for data transfer.
>>>>>>>
>>>>>>> Signed-off-by: Lucas Stach <dev@xxxxxxxxxx>
>>>>>>> Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
>>>>>>> ---
>>>>>>> MAINTAINERS | 7 +
>>>>>>> drivers/mtd/nand/raw/Kconfig | 6 +
>>>>>>> drivers/mtd/nand/raw/Makefile | 1 +
>>>>>>> drivers/mtd/nand/raw/tegra_nand.c | 1248 +++++++++++++++++++++++++++++
>>>>>>> 4 files changed, 1262 insertions(+)
>>>>>>> create mode 100644 drivers/mtd/nand/raw/tegra_nand.c
>>>>>>>
>>>>> [snip]
>>>>>>> +static int tegra_nand_cmd(struct nand_chip *chip,
>>>>>>> + const struct nand_subop *subop)
>>>>>>> +{
>>>>>>> + const struct nand_op_instr *instr;
>>>>>>> + const struct nand_op_instr *instr_data_in = NULL;
>>>>>>> + struct tegra_nand_controller *ctrl = to_tegra_ctrl(chip->controller);
>>>>>>> + unsigned int op_id, size = 0, offset = 0;
>>>>>>> + bool first_cmd = true;
>>>>>>> + u32 reg, cmd = 0;
>>>>>>> + int ret;
>>>>>>> +
>>>>>>> + for (op_id = 0; op_id < subop->ninstrs; op_id++) {
>>>>>>> + unsigned int naddrs, i;
>>>>>>> + const u8 *addrs;
>>>>>>> + u32 addr1 = 0, addr2 = 0;
>>>>>>> +
>>>>>>> + instr = &subop->instrs[op_id];
>>>>>>> +
>>>>>>> + switch (instr->type) {
>>>>>>> + case NAND_OP_CMD_INSTR:
>>>>>>> + if (first_cmd) {
>>>>>>> + cmd |= COMMAND_CLE;
>>>>>>> + writel_relaxed(instr->ctx.cmd.opcode,
>>>>>>> + ctrl->regs + CMD_REG1);
>>>>>>> + } else {
>>>>>>> + cmd |= COMMAND_SEC_CMD;
>>>>>>> + writel_relaxed(instr->ctx.cmd.opcode,
>>>>>>> + ctrl->regs + CMD_REG2);
>>>>>>> + }
>>>>>>> + first_cmd = false;
>>>>>>> + break;
>>>>>>> + case NAND_OP_ADDR_INSTR:
>>>>>>> + offset = nand_subop_get_addr_start_off(subop, op_id);
>>>>>>> + naddrs = nand_subop_get_num_addr_cyc(subop, op_id);
>>>>>>> + addrs = &instr->ctx.addr.addrs[offset];
>>>>>>> +
>>>>>>> + cmd |= COMMAND_ALE | COMMAND_ALE_SIZE(naddrs);
>>>>>>> + for (i = 0; i < min_t(unsigned int, 4, naddrs); i++)
>>>>>>> + addr1 |= *addrs++ << (BITS_PER_BYTE * i);
>>>>>>> + naddrs -= i;
>>>>>>> + for (i = 0; i < min_t(unsigned int, 4, naddrs); i++)
>>>>>>> + addr2 |= *addrs++ << (BITS_PER_BYTE * i);
>>>>>>> + writel_relaxed(addr1, ctrl->regs + ADDR_REG1);
>>>>>>> + writel_relaxed(addr2, ctrl->regs + ADDR_REG2);
>>>>>>> + break;
>>>>>>> +
>>>>>>> + case NAND_OP_DATA_IN_INSTR:
>>>>>>> + size = nand_subop_get_data_len(subop, op_id);
>>>>>>> + offset = nand_subop_get_data_start_off(subop, op_id);
>>>>>>> +
>>>>>>> + cmd |= COMMAND_TRANS_SIZE(size) | COMMAND_PIO |
>>>>>>> + COMMAND_RX | COMMAND_A_VALID;
>>>>>>> +
>>>>>>> + instr_data_in = instr;
>>>>>>> + break;
>>>>>>> +
>>>>>>> + case NAND_OP_DATA_OUT_INSTR:
>>>>>>> + size = nand_subop_get_data_len(subop, op_id);
>>>>>>> + offset = nand_subop_get_data_start_off(subop, op_id);
>>>>>>> +
>>>>>>> + cmd |= COMMAND_TRANS_SIZE(size) | COMMAND_PIO |
>>>>>>> + COMMAND_TX | COMMAND_A_VALID;
>>>>>>> +
>>>>>>> + memcpy(®, instr->ctx.data.buf.out + offset, size);
>>>>>>> + writel_relaxed(reg, ctrl->regs + RESP);
>>>>>>> +
>>>>>>> + break;
>>>>>>> + case NAND_OP_WAITRDY_INSTR:
>>>>>>> + cmd |= COMMAND_RBSY_CHK;
>>>>>>> + break;
>>>>>>> +
>>>>>>> + }
>>>>>>> + }
>>>>>>> +
>>>>>>> + cmd |= COMMAND_GO | COMMAND_CE(ctrl->cur_cs);
>>>>>>> + writel_relaxed(cmd, ctrl->regs + COMMAND);
>>>>>>> + ret = wait_for_completion_io_timeout(&ctrl->command_complete,
>>>>>>> + msecs_to_jiffies(500));
>>>>>>
>>>>>> It's not obvious to me whether _io_ variant is appropriate to use here, would
>>>>>> be nice if somebody could clarify that. Maybe block/ already does the IO
>>>>>> accounting itself and hence the IO time would be counted twice in that case.
>>>>>
>>>>> Good that you bring this up.
>>>>>
>>>>> I don't think that there is any higher layer which could take care of
>>>>> accounting. Usually, with raw nand there is no block layer involved
>>>>> anyway.
>>>>>
>>>>> In a quick test it seems that only when using wait_for_completion_io I/O
>>>>> is properly accounted in the "wait" section of top.
>>>>>
>>>>> So far only a single driver (omap2) used the _io variant, but I think it
>>>>> is the right thing to do! After all, it is I/O...
>>>>>
>>>>> Boris or any other MTD maintainer, any comment on this?
>>>>
>>>> Given this definition of io_schedule_timeout() [1] (which is used when
>>>> you call wait_for_completion_io_timeout()), I'd say it's not useful to
>>>> use the _io_ version, simply because MTD devs are not exposed as blk
>>>> devices, and thus don't need the blk_schedule_flush_plug() that is done
>>>> is io_schedule_prepare(). But that also means MTD I/Os are not
>>>> accounted as I/Os :-(.
>>>
>>> Documentation of wait_for_completion_io says:
>>> "The caller is accounted as waiting for IO (which traditionally means
>>> blkio only)."
>>>
>>> Which sounds as if it using _io is only an accounting thing...
>>
>> Yes, you should only use it for waiting for IO off a system call
>> read path. So block IO, or file system IO. Don't use it for internal
>> IO that isn't related to that.
>
> I guess that would be the case here, since MTD page read/writes are
> typically file system IOs (e.g. UBIFS).
>
> The problem is just that is not block related at all since it uses the
> MTD subsystem... And it seems that the _io variants besides accounting,
> also take a role in the block subsystems device plugging mechanism. What
> is unclear to me if using the _io variant from the MTD subsystem
> potentially disturbs the plugging mechanism...
No, it has nothing to do with plugging at the block level. So if you're
doing regular user IO, then you should use the _io variants.
--
Jens Axboe
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