Message-ID: <20231004005525.3f406823@xps-13>
Date:   Wed, 4 Oct 2023 00:55:25 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     William Zhang <william.zhang@...adcom.com>
Cc:     dregan@...l.com, bcm-kernel-feedback-list@...adcom.com,
        linux-mtd@...ts.infradead.org, f.fainelli@...il.com,
        rafal@...ecki.pl, joel.peshkin@...adcom.com,
        computersforpeace@...il.com, dan.beygelman@...adcom.com,
        frieder.schrempf@...tron.de, linux-kernel@...r.kernel.org,
        vigneshr@...com, richard@....at, bbrezillon@...nel.org,
        kdasu.kdev@...il.com
Subject: Re: [PATCH v2] mtd: rawnand: brcmnand: Initial exec_op
 implementation

Hi William,

william.zhang@...adcom.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@...adcom.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@...l.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@...l.com>
> >>>> Reviewed-by: William Zhang <william.zhang@...adcom.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.

Thanks,
Miquèl

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