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Subject: Re: [PATCH v2] mtd: rawnand: brcmnand: Initial exec_op implementation
To:     Miquel Raynal <miquel.raynal@bootlin.com>
Cc:     dregan@mail.com, bcm-kernel-feedback-list@broadcom.com,
        linux-mtd@lists.infradead.org, f.fainelli@gmail.com,
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        vigneshr@ti.com, richard@nod.at, bbrezillon@kernel.org,
        kdasu.kdev@gmail.com
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From:   William Zhang <william.zhang@broadcom.com>
Message-ID: <0f6bd61c-19ed-8153-1763-eef2498726c7@broadcom.com>
Date:   Tue, 3 Oct 2023 21:47:16 -0700
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On 10/03/2023 03:55 PM, Miquel Raynal wrote:
> Hi William,
> 
> william.zhang@broadcom.com wrote on Tue, 3 Oct 2023 11:46:25 -0700:
> 
>> Hi Miquel,
>>
>> On 10/03/2023 02:28 AM, Miquel Raynal wrote:
>>> Hi William,
>>>
>>> william.zhang@broadcom.com wrote on Mon, 2 Oct 2023 12:57:01 -0700:
>>>    
>>>> Hi Miquel,
>>>>
>>>> On 10/02/2023 05:35 AM, Miquel Raynal wrote:
>>>>> Hi David,
>>>>>
>>>>> dregan@mail.com wrote on Sat, 30 Sep 2023 03:57:35 +0200:
>>>>>     >>>> Initial exec_op implementation for Broadcom STB, Broadband and iProc SoC
>>>>>> This adds exec_op and removes the legacy interface.
>>>>>>
>>>>>> Signed-off-by: David Regan <dregan@mail.com>
>>>>>> Reviewed-by: William Zhang <william.zhang@broadcom.com>
>>>>>>
>>>>>> ---
>>>>>>    >>>
>>>>> ...
>>>>>     >>>> +static int brcmnand_parser_exec_matched_op(struct nand_chip *chip,
>>>>>> +					 const struct nand_subop *subop)
>>>>>> +{
>>>>>> +	struct brcmnand_host *host = nand_get_controller_data(chip);
>>>>>> +	struct brcmnand_controller *ctrl = host->ctrl;
>>>>>> +	struct mtd_info *mtd = nand_to_mtd(chip);
>>>>>> +	const struct nand_op_instr *instr = &subop->instrs[0];
>>>>>> +	unsigned int i;
>>>>>> +	int ret = 0;
>>>>>> +
>>>>>> +	for (i = 0; i < subop->ninstrs; i++) {
>>>>>> +		instr = &subop->instrs[i];
>>>>>> +
>>>>>> +		if ((instr->type == NAND_OP_CMD_INSTR) &&
>>>>>> +			(instr->ctx.cmd.opcode == NAND_CMD_STATUS))
>>>>>> +			ctrl->status_cmd = 1;
>>>>>> +		else if (ctrl->status_cmd && (instr->type == NAND_OP_DATA_IN_INSTR)) {
>>>>>> +			/*
>>>>>> +			 * need to fake the nand device write protect because nand_base does a
>>>>>> +			 * nand_check_wp which calls nand_status_op NAND_CMD_STATUS which checks
>>>>>> +			 * that the nand is not write protected before an operation starts.
>>>>>> +			 * The problem with this is it's done outside exec_op so the nand is
>>>>>> +			 * write protected and this check will fail until the write or erase
>>>>>> +			 * or write back operation actually happens where we turn off wp.
>>>>>> +			 */
>>>>>> +			u8 *in;
>>>>>> +
>>>>>> +			ctrl->status_cmd = 0;
>>>>>> +
>>>>>> +			instr = &subop->instrs[i];
>>>>>> +			in = instr->ctx.data.buf.in;
>>>>>> +			in[0] = brcmnand_status(host) | NAND_STATUS_WP; /* hide WP status */
>>>>>
>>>>> I don't understand why you are faking the WP bit. If it's set,
>>>>> brcmnand_status() should return it and you should not care about it. If
>>>>> it's not however, can you please give me the path used when we have
>>>>> this issue? Either we need to modify the core or we need to provide
>>>>> additional helpers in this driver to circumvent the faulty path.
>>>>
>>>> The reason we have to hide wp status for status command is because
>>>> nand_base calls nand_check_wp at the very beginning of write and erase
>>>> function. This applies to both exec_op path and legacy path. With
>>>> Broadcom nand controller and most of our board design using the WP pin
>>>> and have it asserted by default, the nand_check_wp function will fail
>>>> and write/erase aborts.  This workaround has been there before this
>>>> exec_op patch.
>>>>
>>>> I agree it is ugly and better to be addressed in the nand base code. And
>>>> I understand Broadcom's WP approach may sound a bit over cautious but we
>>>> want to make sure no spurious erase/write can happen under any
>>>> circumstance except software explicitly want to write and erase.  WP is
>>>> standard nand chip pin and I think most the nand controller has that
>>>> that pin in the design too but it is possible it is not used and
>>>> bootloader can de-assert the pin and have a always-writable nand flash
>>>> for linux. So maybe we can add nand controller dts option "nand-use-wp".
>>>> If this property exist and set to 1,  wp control is in use and nand
>>>> driver need to control the pin on/ff as needed when doing write and
>>>> erase function. Also nand base code should not call nand_check_wp when
>>>> wp is in use. Then we can remove the faking WP status workaround.
>>>>   
>>>>>     >>>> +		} else if (instr->type == NAND_OP_WAITRDY_INSTR) {
>>>>>> +			ret = bcmnand_ctrl_poll_status(host, NAND_CTRL_RDY, NAND_CTRL_RDY, 0);
>>>>>> +			if (ctrl->wp_cmd) {
>>>>>> +				ctrl->wp_cmd = 0;
>>>>>> +				brcmnand_wp(mtd, 1);
>>>>>
>>>>> This ideally should disappear.
>>>>>     >> Maybe we can have the destructive operation patch from Borris.
>>>> Controller driver still need to assert/deassert the pin if it uses nand
>>>> wp feature but at least it does not need to guess the op code.
>>>
>>> Ah, yeah, I get it.
>>>
>>> Please be my guest, you can revive this patch series (might need light
>>> tweaking, nothing big) and also take inspiration from it if necessary:
>>> https://github.com/bbrezillon/linux/commit/e612e1f2c69a33ac5f2c91d13669f0f172d58717
>>> https://github.com/bbrezillon/linux/commit/4ec6f8d8d83f5aaca5d1877f02d48da96d41fcba
>>> https://github.com/bbrezillon/linux/commit/11b4acffd761c4928652d7028d19fcd6f45e4696
>>>    
>> Sure we will incorporate the destructive operation patch and provide a
>> new revision.
>>
>> The WP status workaround will stay at least for this change. If you
>> think my suggestion using a dts setting above is okay, we can provide a
>> patch for that as well.  Or if you have any other idea or suggestion,
>> we'd like to hear too.
> 
> I thought this was not needed as Boris initial conversion did not need
> it. The goal is to get rid of this workaround.
> Boris' initial patch did remove that workaround but it will break the
board that uses WP pin because the nand_check_wp run before the exec_op 
and status returned is write-protected in the erase and write function.
I explained that above and you can see the code here:
https://elixir.bootlin.com/linux/v6.6-rc4/source/drivers/mtd/nand/raw/nand_base.c#L4599

I agree with your goal to remove this workaround and we have suggested
one possible fix but we are also open to any other solution.


> Thanks,
> Miquèl
> 

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