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Subject: Re: [PATCH v2] mtd: rawnand: brcmnand: Initial exec_op implementation
From:   William Zhang <william.zhang@broadcom.com>
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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        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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Message-ID: <0c72dbb4-8ee5-c9b0-b029-9689e9d72f5e@broadcom.com>
Date:   Thu, 5 Oct 2023 17:42:21 -0700
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Hi Miquel,

On 10/03/2023 09:47 PM, William Zhang wrote:
> 
> 
> 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.
> 
We have integrated the destructive operation patch and are ready for the
v3.  If you don't think my proposal on the WP status fix is a good idea,
can we get this exce_op conversion patch series going first?  After all,
we don't modify the WP status handling behavior in this patch. We can
fix it in another patch whenever we agree on a solution.  Please let me
know and thanks a lot for all your comments and thoughts.

Thanks,
William

> 
>> Thanks,
>> Miquèl
>>

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