On Mon, 17 May 2021 11:24:25 +0200
Patrice CHOTARD [off-list ref] wrote:

Hi Boris

On 5/17/21 9:41 AM, Boris Brezillon wrote:

quoted

On Fri, 7 May 2021 15:17:54 +0200
[off-list ref] wrote:
  

quoted

+/**
+ * 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.

quoted

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.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel