Re: [PATCH v2 1/3] spi: spi-mem: add automatic poll status functions

[Boris Brezillon]

On Mon, 17 May 2021 11:24:25 +0200
Patrice CHOTARD <patrice.chotard@xxxxxxxxxxx> wrote:

> Hi Boris
> 
> On 5/17/21 9:41 AM, Boris Brezillon wrote:
> > On Fri, 7 May 2021 15:17:54 +0200
> > <patrice.chotard@xxxxxxxxxxx> wrote:
> >   
> >> +/**
> >> + * spi_mem_poll_status() - Poll memory device status
> >> + * @mem: SPI memory device
> >> + * @op: the memory operation to execute
> >> + * @mask: status bitmask to ckeck
> >> + * @match: (status & mask) expected value
> >> + * @timeout_ms: timeout in milliseconds
> >> + *
> >> + * This function send a polling status request to the controller driver
> >> + *
> >> + * Return: 0 in case of success, -ETIMEDOUT in case of error,
> >> + *         -EOPNOTSUPP if not supported.
> >> + */
> >> +int spi_mem_poll_status(struct spi_mem *mem,
> >> +			const struct spi_mem_op *op,
> >> +			u16 mask, u16 match, u16 timeout_ms)  
> > 
> > Maybe you should pass a delay_us too, to poll the status at the right
> > rate in the SW-based case (can also be used by drivers if they need to  
> 
> Ok, i will add a polling_rate_us parameter to poll_status() callback,
> even if in STM32 driver case we will not use it, i agree it should be useful 
> depending of driver's implementation.
> 
> > configure the polling rate). You could also add an initial_delay_us to
> > avoid polling the status too early: an erase operation will take longer
> > than a write which will take longer than a read. No need to check the
> > status just after issuing the command, especially if the polling is
> > done in SW. Those 2 arguments should also be passed to the driver.  
> 
> Regarding the addition of an initial_delay_us. We got two solution:
>   - use the same polling rate already used by read_poll_timeout() and 
>     set read_poll_timeout()'s sleep_before_read parameter to true (in our case 20 us
>     will be used as initial delay and as polling rate).
> 
>   - add an udelay(initial_delay_us) or even better usleep_range(initial_delay_us,
>     initial_delay_us + delta) before calling read_poll_timeout().
> 
> I imagine you prefer the second solution ?

Yep, you might want to use udelay() when the delay is small and
usleep_range() otherwise.

> 
> By adding polling_rate_us and initial_delay_us parameters to 
> spi_mem_poll_status(), it implies to update all spinand_wait() calls for 
> different operations (reset, read page, write page, erase) with respective  
> initial_delay_us/polling_rate_us values for spi_mem_poll_status()'s parameters.
> 
> Can you provide adequate initial_delay_us and polling rate_us for each operation type ?.

If I refer to the datasheets I have,

tBERS (erase) 1ms to 4ms
tPROG 300us to 400us
tREAD 25us to 100us

Let's assume we want to minimize the latency, I'd recommend dividing
the min value by 4 for the initial delay, and dividing it by 20 for the
poll delay, which gives:

ERASE -> initial_delay = 250us, poll_delay = 50us
PROG -> initial_delay = 100us, poll_delay = 20us
READ -> initial_delay = 6us, poll_delay = 5us

Of course, that'd be even better if we were able to extract this
information from the NAND ID (or ONFI table), but I guess we can live
with those optimistic values in the meantime.