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

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Message-ID: <45ee6378-271d-aeb5-90ea-ed2e0673f3fb@foss.st.com>
Date:   Mon, 17 May 2021 14:04:58 +0200
From:   Patrice CHOTARD <patrice.chotard@...s.st.com>
To:     Boris Brezillon <boris.brezillon@...labora.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 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

another remark, it should be:  PROG -> initial_delay = 75 us (300 / 4) , poll_delay = 15us ( 300 / 20)

Patrice

> 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.
>