RE: [LINUX PATCH v10 2/2] mtd: rawnand: arasan: Add support for Arasan NAND Flash Controller

[Naga Sureshkumar Relli <nagasure@xilinx.com>]

Hi Boris,

Thanks for the review.

> -----Original Message-----
> From: Boris Brezillon [mailto:boris.brezillon@bootlin.com]
> Sent: Friday, August 17, 2018 11:29 PM
> To: Naga Sureshkumar Relli <nagasure@xilinx.com>
> Cc: miquel.raynal@bootlin.com; richard@nod.at; dwmw2@infradead.org;
> computersforpeace@gmail.com; marek.vasut@gmail.com; kyungmin.park@samsung.com;
> absahu@codeaurora.org; peterpandong@micron.com; frieder.schrempf@exceet.de; linux-
> mtd@lists.infradead.org; linux-kernel@vger.kernel.org; Michal Simek <michals@xilinx.com>;
> nagasureshkumarrelli@gmail.com
> Subject: Re: [LINUX PATCH v10 2/2] mtd: rawnand: arasan: Add support for Arasan
> NAND Flash Controller
> 
> Hi Naga,
> 
> On Fri, 17 Aug 2018 18:49:24 +0530
> Naga Sureshkumar Relli <naga.sureshkumar.relli@xilinx.com> wrote:
> 
> > +static int anfc_exec_op_cmd(struct nand_chip *chip,
> > +				   const struct nand_subop *subop) {
> > +	const struct nand_op_instr *instr;
> > +	struct anfc_op nfc_op = {};
> > +	struct anfc_nand_chip *achip = to_anfc_nand(chip);
> > +	struct anfc_nand_controller *nfc = to_anfc(chip->controller);
> > +	struct mtd_info *mtd = nand_to_mtd(chip);
> > +	u32 addrcycles;
> > +	unsigned int op_id, len = 0;
> > +	bool reading;
> > +
> > +	anfc_parse_instructions(chip, subop, &nfc_op);
> > +	instr = nfc_op.data_instr;
> > +	op_id = nfc_op.data_instr_idx;
> > +	if (nfc_op.data_instr)
> > +		len = nand_subop_get_data_len(subop, op_id);
> > +
> > +	/*
> > +	 * The switch case is to prepare a command and to set page/column
> > +	 * address. Arasan NAND controller has program register(Off: 0x10)),
> > +	 * which needs to be set for every command.
> > +	 * Ex: When NAND_CMD_RESET is issued, then we need to set reset bit
> > +	 * in program_register. etc..
> > +	 */
> > +	switch (nfc_op.cmnds[0]) {
> > +	case NAND_CMD_SEQIN:
> > +		addrcycles = achip->raddr_cycles + achip->caddr_cycles;
> > +
> > +		anfc_prepare_cmd(nfc, nfc_op.cmnds[0], NAND_CMD_PAGEPROG, 1,
> > +				 mtd->writesize, addrcycles);
> > +		anfc_setpagecoladdr(nfc, nfc_op.row, nfc_op.col);
> > +		break;
> > +	case NAND_CMD_READOOB:
> > +		nfc_op.col += mtd->writesize;
> > +	case NAND_CMD_READ0:
> > +	case NAND_CMD_READ1:
> > +		addrcycles = achip->raddr_cycles + achip->caddr_cycles;
> > +		anfc_prepare_cmd(nfc, NAND_CMD_READ0, NAND_CMD_READSTART,
> 1,
> > +				 mtd->writesize, addrcycles);
> > +		anfc_setpagecoladdr(nfc, nfc_op.row, nfc_op.col);
> > +		if (!nfc_op.data_instr)
> > +			return 0;
> > +
> > +		anfc_read_data_op(mtd, instr->ctx.data.buf.in, len);
> > +		break;
> > +	case NAND_CMD_RNDOUT:
> > +		anfc_prepare_cmd(nfc, nfc_op.cmnds[0], NAND_CMD_RNDOUTSTART, 1,
> > +				 mtd->writesize, 2);
> > +		anfc_setpagecoladdr(nfc, nfc_op.row, nfc_op.col);
> > +		nfc->prog = PROG_PGRD;
> > +		break;
> > +	case NAND_CMD_PARAM:
> > +		anfc_prepare_cmd(nfc, nfc_op.cmnds[0], 0, 0, 0, 1);
> > +		anfc_setpagecoladdr(nfc, nfc_op.row, nfc_op.col);
> > +		nfc->prog = PROG_RDPARAM;
> > +		break;
> > +	case NAND_CMD_READID:
> > +		anfc_prepare_cmd(nfc, nfc_op.cmnds[0], 0, 0, 0, 1);
> > +		anfc_setpagecoladdr(nfc, nfc_op.row, nfc_op.col);
> > +		nfc->prog = PROG_RDID;
> > +		break;
> > +	case NAND_CMD_GET_FEATURES:
> > +		anfc_prepare_cmd(nfc, nfc_op.cmnds[0], 0, 0, 0, 1);
> > +		anfc_setpagecoladdr(nfc, nfc_op.row, nfc_op.col);
> > +		nfc->prog = PROG_GET_FEATURE;
> > +		break;
> > +	case NAND_CMD_SET_FEATURES:
> > +		anfc_prepare_cmd(nfc, nfc_op.cmnds[0], 0, 0, 0, 1);
> > +		anfc_setpagecoladdr(nfc, nfc_op.row, nfc_op.col);
> > +		nfc->prog = PROG_SET_FEATURE;
> > +		break;
> > +	case NAND_CMD_ERASE1:
> > +		anfc_erase_function(chip, nfc_op);
> > +		break;
> > +	default:
> > +		break;
> > +	}
> 
> Looks like you have one of these smart controllers where everything is hardcoded and new
> commands (like vendor specific commands) can't be supported, and we're back to abusing -
> >exec_op(), just like ->cmdfunc() was abused.
Actually hardcoding commands with ->exec_op() interface in the driver is really looking weird.
I agree with that.
But as per the spec, for every command, we need to set respective bit in PROG_REG and because
Of this, we need to track the commands for each exec_op() call.
> 
> Don't you have a way to send raw CMD/ADDR/DATA cycles? If not, then we'll have to
> consider other options, because I don't want to go back to the situation we are in with -
> >cmdfunc().
As I said above, for each command we need to set a bit in PROG_REG, to initiate the operation.
The only conflicting thing is that, setting a respective bit in PROG_REG based on the command
Needs command tracking. 
> 
> Maybe I already asked, but is there a public spec for this IP?
I didn't find any public spec for this IP, but you can find the register data base at below link
https://www.xilinx.com/html_docs/registers/ug1087/ug1087-zynq-ultrascale-registers.html
and click on NAND.
There we have Command Reg(Off: 0x0C) and Program Reg(Off: 0x10), which describes the usage.

Also not in depth but at least something is documented in TRM
https://www.xilinx.com/support/documentation/user_guides/ug1085-zynq-ultrascale-trm.pdf
we can find the programming model in chapter 25.
Please let me know if I missed anything.

Thanks,
Naga Sureshkumar Relli.
> 
> Thanks,
> 
> Boris