Re: [RFC PATCH v2 2/2] mtd: rawnand: meson: add support for Amlogic NAND flash controller

[Liang Yang]

Hi Boris,

There is a question below. please see my comments.

Thanks.

On 8/17/2018 9:56 PM, Boris Brezillon wrote:
> On Fri, 17 Aug 2018 21:03:59 +0800
> Liang Yang <liang.yang@xxxxxxxxxxx> wrote:
>
> > Hi Boris,
> > On 2018/8/2 5:50, Boris Brezillon wrote:
> >
> > > Hi Yixun,
> > >
> > > On Thu, 19 Jul 2018 17:46:12 +0800
> > > Yixun Lan <yixun.lan@xxxxxxxxxxx> wrote:
> > >
> > > I haven't finished reviewing the driver yet (I'll try to do that later
> > > this week), but I already pointed a few things to fix/improve.
> > >   
> > > > +
> > > > +static int meson_nfc_exec_op(struct nand_chip *chip,
> > > > +			     const struct nand_operation *op, bool check_only)
> > > > +{
> > > > +	struct mtd_info *mtd = nand_to_mtd(chip);
> > > > +	struct meson_nfc *nfc = nand_get_controller_data(chip);
> > > > +	const struct nand_op_instr *instr = NULL;
> > > > +	int ret = 0, cmd;
> > > > +	unsigned int op_id;
> > > > +	int i;
> > > > +
> > > > +	for (op_id = 0; op_id < op->ninstrs; op_id++) {
> > > > +		instr = &op->instrs[op_id];
> > > > +		switch (instr->type) {
> > > > +		case NAND_OP_CMD_INSTR:
> > > > +			cmd = nfc->param.chip_select | NFC_CMD_CLE;
> > > > +			cmd |= instr->ctx.cmd.opcode & 0xff;
> > > > +			writel(cmd, nfc->reg_base + NFC_REG_CMD);
> > > > +			meson_nfc_cmd_idle(nfc, NAND_TWB_TIME_CYCLE);
> >
> > > > +			meson_nfc_drain_cmd(nfc);
> > > I don't know exactly how the NAND controller works, but it's usually
> > > > +			break;
> > > > +
> > > > +		case NAND_OP_ADDR_INSTR:
> > > > +			for (i = 0; i < instr->ctx.addr.naddrs; i++) {
> > > > +				cmd = nfc->param.chip_select | NFC_CMD_ALE;
> > > > +				cmd |= instr->ctx.addr.addrs[i] & 0xff;
> > > > +				writel(cmd, nfc->reg_base + NFC_REG_CMD);
> > > > +			}
> > > > +			break;
> > > > +
> > > > +		case NAND_OP_DATA_IN_INSTR:
> > > > +			meson_nfc_read_buf(mtd, instr->ctx.data.buf.in,
> > > > +					   instr->ctx.data.len);
> > > > +			break;
> > > > +
> > > > +		case NAND_OP_DATA_OUT_INSTR:
> > > > +			meson_nfc_write_buf(mtd, instr->ctx.data.buf.out,
> > > > +					    instr->ctx.data.len);
>
> > > > +			break;
> > > > +
> > > > +		case NAND_OP_WAITRDY_INSTR:
> > > > +			mdelay(instr->ctx.waitrdy.timeout_ms);
> > > > +			ret = nand_soft_waitrdy(chip,
> > > > +						instr->ctx.waitrdy.timeout_ms);
> > > Hm, i'd be surprised if the controller does not have a way to optimize
> > > waits on R/B transitions.
> >
> > When i delete the delay here, erasing operation will be failed.
> > Does it mean NFC send 0x70 to nand device when rb is busy(low)?
>
> I was not even talking about the delay, but yes, mdelay() seems way too
> big. Remember that it's a timeout, and you usually don't have to wait
> that much. You can do ndelay(instr->ctx.delay_ns) before calling
> nand_soft_waitrdy() to make sure tWB is enforced.
>
> Anyway, that's not what I was initially referring to. What I meant is
> that nand_soft_waitrdy() should be replaced by native R/B pin or status
> polling wait logic so that the CPU is released while waiting for a R/B
> transition.
>
> > If so, i will ask our NFC designer for comfirmation or grasping the waveform.
>
> You have to wait tWB, that's for sure.
we have a maximum 32 commands fifo. when command is written into 
NFC_REG_CMD, it doesn't mean that command is executing right now, maybe 
it is buffering on the queue.Assume one ERASE operation, when 2nd 
command(0xd0) is written into NFC_REG_CMD and then come into 
NAND_OP_WAITRDY_INSTR, if I read the RB status by register, it may be 
wrong because 0xd0 may not being executed. it is unusual unless 
buffering two many command.
so it seems that i still need to use nand_soft_waitrdy or wait cmd is 
executed somewhere.
> >