linux-kernel - Re: [PATCH] spi: spi-mem: add statistics support to ->exec

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Message-Id: <CZ41HDHS7WX6.6MJL1O2PBVW1@bootlin.com>
Date: Tue, 13 Feb 2024 16:00:14 +0100
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: "Tudor Ambarus" <tudor.ambarus@...aro.org>, "Mark Brown"
 <broonie@...nel.org>
Cc: <linux-spi@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Dhruva
 Gole" <d-gole@...com>, "Gregory CLEMENT" <gregory.clement@...tlin.com>,
 "Vladimir Kondratiev" <vladimir.kondratiev@...ileye.com>, "Thomas
 Petazzoni" <thomas.petazzoni@...tlin.com>, "Tawfik Bayouk"
 <tawfik.bayouk@...ileye.com>
Subject: Re: [PATCH] spi: spi-mem: add statistics support to ->exec_op()
 calls

Hello Tudor,

On Tue Feb 13, 2024 at 1:39 PM CET, Tudor Ambarus wrote:
> >  /**
> >   * spi_mem_exec_op() - Execute a memory operation
> >   * @mem: the SPI memory
> > @@ -339,8 +383,12 @@ int spi_mem_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
> >  		 * read path) and expect the core to use the regular SPI
> >  		 * interface in other cases.
> >  		 */
> > -		if (!ret || ret != -ENOTSUPP || ret != -EOPNOTSUPP)
> > +		if (!ret || ret != -ENOTSUPP || ret != -EOPNOTSUPP) {
> > +			spi_mem_add_op_stats(ctlr->pcpu_statistics, op, ret);
> > +			spi_mem_add_op_stats(mem->spi->pcpu_statistics, op, ret);
> > +
>
> Would be good to be able to opt out the statistics if one wants it.
>
> SPI NORs can write with a single write op maximum page_size bytes, which
> is typically 256 bytes. And since there are SPI NORs that can run at 400
> MHz, I guess some performance penalty shouldn't be excluded.

I did my testing on a 40 MHz octal SPI NOR with most reads being much
bigger than 256 bytes, so I probably didn't have the fastest setup
indeed.

What shape would that take? A spi-mem DT prop? New field in the SPI
statistics sysfs directory?

Other remarks have been taken into account, thanks!

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com