linux-kernel - Re: [RFC PATCH 3/6] mtd: spi-nor: core: run calibration when initialization is done

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Message-ID: <20220518091931.279c5398@xps-13>
Date:   Wed, 18 May 2022 09:19:31 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Pratyush Yadav <p.yadav@...com>
Cc:     Nishanth Menon <nm@...com>, Tero Kristo <kristo@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Michael Walle <michael@...le.cc>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Mark Brown <broonie@...nel.org>,
        Cédric Le Goater <clg@...d.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-mtd@...ts.infradead.org>, <linux-spi@...r.kernel.org>
Subject: Re: [RFC PATCH 3/6] mtd: spi-nor: core: run calibration when
 initialization is done

Hi Pratyush,

p.yadav@...com wrote on Wed, 18 May 2022 11:37:05 +0530:

> +Cedric
> 
> On 17/05/22 04:02PM, Miquel Raynal wrote:
> > Hi Pratyush,
> > 
> > p.yadav@...com wrote on Fri, 12 Mar 2021 00:42:13 +0530:
> >   
> > > Once the flash is initialized tell the controller it can run
> > > calibration procedures if needed. This can be useful when calibration is
> > > needed to run at higher clock speeds.
> > > 
> > > Signed-off-by: Pratyush Yadav <p.yadav@...com>
> > > ---
> > >  drivers/mtd/spi-nor/core.c | 12 ++++++++++--
> > >  1 file changed, 10 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> > > index 88888df009f0..e0cbcaf1be89 100644
> > > --- a/drivers/mtd/spi-nor/core.c
> > > +++ b/drivers/mtd/spi-nor/core.c
> > > @@ -3650,6 +3650,7 @@ static int spi_nor_probe(struct spi_mem *spimem)
> > >  	 * checking what's really supported using spi_mem_supports_op().
> > >  	 */
> > >  	const struct spi_nor_hwcaps hwcaps = { .mask = SNOR_HWCAPS_ALL };
> > > +	struct spi_mem_op op;
> > >  	char *flash_name;
> > >  	int ret;
> > >  
> > > @@ -3709,8 +3710,15 @@ static int spi_nor_probe(struct spi_mem *spimem)
> > >  	if (ret)
> > >  		return ret;
> > >  
> > > -	return mtd_device_register(&nor->mtd, data ? data->parts : NULL,
> > > -				   data ? data->nr_parts : 0);
> > > +	ret = mtd_device_register(&nor->mtd, data ? data->parts : NULL,
> > > +				  data ? data->nr_parts : 0);
> > > +	if (ret)
> > > +		return ret;
> > > +
> > > +	op = spi_nor_spimem_get_read_op(nor);  
> > 
> > Isn't this too specific? I really don't know much about spi-nors, but I
> > find odd to have this op being created here, why not moving this into
> > the _do_calibration() helper?  
> 
> Maybe the naming confused you but this is a function in the SPI NOR 
> core, not in SPI MEM. SPI NOR supports both SPI MEM based controllers 
> and "legacy" controllers, so the convention is to add the "spimem" 
> prefix before SPI MEM specific functions. So I don't get the comment 
> about it being too specific. It is too specific to what?

Mmh right, it's fine then.

> 
> And how can spi_mem_do_calibration() know what op the flash uses to read 
> data? SPI NOR or SPI NAND would know it, but not SPI MEM. That is why we 
> pass in that information to spi_mem_do_calibration().

But here the op is "spi-nor wide", I would have expected a
per-device op. But that is not a big deal, that is something that can
also be updated later if needed I guess.

One last question, is there something that mtd_device_register() does
that is really needed for the calibration to work? Otherwise I would
rather prefer to have that calibration happening before the user gets
access to the device.

> 
> >   
> > > +	spi_mem_do_calibration(nor->spimem, &op);  
> > 
> > A warning/info upon calibration error (not on the absence of the hook)
> > would be nice?  
> 
> Yes, agreed.
> 
> >   
> > > +
> > > +	return 0;
> > >  }
> > >  
> > >  static int spi_nor_remove(struct spi_mem *spimem)  
> > 
> > Otherwise I like the overall idea.  
> 
> Thanks for reviewing.
> 
> > 
> > Thanks,
> > Miquèl  
> 


Thanks,
Miquèl