Re: [PATCH v2] mtd: rawnand: brcmnand: Initial exec_op implementation

[Miquel Raynal <miquel.raynal@bootlin.com>]

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

Thanks,
Miquèl

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