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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,
        rafal@milecki.pl, joel.peshkin@broadcom.com,
        computersforpeace@gmail.com, dan.beygelman@broadcom.com,
        frieder.schrempf@kontron.de, linux-kernel@vger.kernel.org,
        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: <37416f2e-f150-cc8f-76bd-3d54f9e25d08@broadcom.com>
Date:   Tue, 3 Oct 2023 11:46:25 -0700
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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.


> Thanks,
> Miquèl
> 

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