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

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Message-ID: <20210517142418.7689c01f@collabora.com>
Date:   Mon, 17 May 2021 14:24:18 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Patrice CHOTARD <patrice.chotard@...s.st.com>
Cc:     Mark Brown <broonie@...nel.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        <linux-mtd@...ts.infradead.org>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        <linux-spi@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <christophe.kerello@...s.st.com>
Subject: Re: [PATCH v2 1/3] spi: spi-mem: add automatic poll status
 functions

On Mon, 17 May 2021 13:59:54 +0200
Patrice CHOTARD <patrice.chotard@...s.st.com> wrote:

> Hi 
> 
> On 5/17/21 1:25 PM, Boris Brezillon wrote:
> > On Mon, 17 May 2021 11:24:25 +0200
> > Patrice CHOTARD <patrice.chotard@...s.st.com> wrote:
> >   
> >> Hi Boris
> >>
> >> On 5/17/21 9:41 AM, Boris Brezillon wrote:  
> >>> On Fri, 7 May 2021 15:17:54 +0200
> >>> <patrice.chotard@...s.st.com> 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  
> 
> 
> What about RESET ? we also need an initial and poll delay too (see spinand_reset_op() )

5us/10us/500us if the device is respectively
reading/programming/erasing when the RESET occurs. Since we always
issue a RESET when the device is IDLE, I'd recommend going for 5us for
both the initial_delay and poll_delay.

> 
> > 
> > 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.
> >   
> 
> Thanks
> Patrice