linux-kernel - Re: [PATCH 09/20] regmap: _regmap_raw_write fix for busses without write()

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Message-ID: <20150812130518.GM19600@pengutronix.de>
Date:	Wed, 12 Aug 2015 15:05:18 +0200
From:	Markus Pargmann <mpa@...gutronix.de>
To:	Mark Brown <broonie@...nel.org>
Cc:	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jonathan Cameron <jic23@...nel.org>, kernel@...gutronix.de,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 09/20] regmap: _regmap_raw_write fix for busses without
 write()

On Wed, Aug 12, 2015 at 01:34:06PM +0100, Mark Brown wrote:
> On Wed, Aug 12, 2015 at 02:20:11PM +0200, Markus Pargmann wrote:
> > On Wed, Aug 12, 2015 at 12:20:35PM +0100, Mark Brown wrote:
> > > On Wed, Aug 12, 2015 at 12:12:34PM +0200, Markus Pargmann wrote:
> > > 
> > > > @@ -1229,6 +1229,11 @@ int _regmap_raw_write(struct regmap *map, unsigned int reg,
> > > >  		}
> > > >  	}
> > > >  
> > > > +	if (!map->bus->write && val_len == map->format.val_bytes) {
> > > > +		ret = _regmap_bus_reg_write(map, reg, *(unsigned int *)val);
> > > > +		return ret;
> > > > +	}
> 
> > > This is broken - you can't use a raw value as a register value.  The
> 
> > I am not sure what you mean here?
> 
> > The register value given to _regmap_raw_write is the real register
> > value, not formatted differenty. This is given directly towards
> > bus->reg_write() which should handle the rest.
> 
> I mean the value for the register, not the register address.
> 
> > At least that's how I understood the code. For example regmap_read()
> > directly calls _regmap_read() which in turn calls directly
> > bus->reg_read() without any formating.
> 
> You're adding this code to regmap_raw_write() which takes raw register
> values for the device, not unsigned integers.

Ah yes, I see.

> 
> > > endianness of the device may not be the same as the endianness of the
> > > system and you can't cast a value to unsigned int, the value may be of
> > > any size.
> 
> > Yes right. On the other hand if bus->read() and bus->write() was not set
> > in the init method (before this patch series) no formatting functions at
> > all were assigned. So it was always ignored for bus->reg_read() and
> > bus->reg_write()?!
> 
> I'm not sure what the "it" you're talking about here is, sorry.  There
> are unsupported features in the API especially for cases that don't make
> a huge amount of sense, the error handling isn't always complete.  It
> sounds like you might be trying to support one of these nonsensical
> cases - it's not obvious what raw I/O on a device where we don't know
> the raw format of the device should mean or how anything could sensibly
> use that.

The bus and the regmap user are separate. So as a regmap user, I am not
able to know if the bus the device is connected to actually supports raw
reads/writes. At least it should not fail with a null pointer when using
these functions anyway so yes error handling is missing a bit here.

Also the real use of this function is regmap_bulk_write() which always
uses _regmap_raw_write() regardless of a missing bus->write() function.
So regmap_bulk_write will fail for those as well and this should be
supported.

But it is probably better to handle this in regmap_bulk_write() and
add a simple check for bus->write() here.

Best Regards,

Markus

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