linux-kernel - Re: Regmap bulk read styles.

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Message-ID: <4E64EC7C.5010005@cam.ac.uk>
Date:	Mon, 05 Sep 2011 16:36:28 +0100
From:	Jonathan Cameron <jic23@....ac.uk>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Regmap bulk read styles.

On 09/05/11 16:19, Mark Brown wrote:
> On Mon, Sep 05, 2011 at 03:49:14PM +0100, Jonathan Cameron wrote:
> 
>> The burst read is pretty much what you have covered by
>> regmap_bulk_read. I assume an implementation for spi
>> doing
> 
>> TX Addr1 XXXXX XXXXX XXXXX XXXXX
>> RX XXXXX Data1 Data2 Data3 Data4 ...
> 
>> would be general enough to be worth providing? Any device
>> that doesn't understand this should simply not use it.
> 
> Yes, that's the assumption the code is making for all buses.
Cool. If no one else does it in the meantime I'll add that one.
> 
>> The second is more interesting.  It actually looks quite like
>> your gather write.  We have a set of registers that we need
>> to read.  A classic example is that a coherent set will only
>> be received (e.g. valid at an instant in time) if we read
>> all channels of an accelerometer in one go (between chip selects).
> 
>> Would you be in favour of an interface to handle this use case
>> or is it better just to bypass regmap for this use case?
>> (which would be a pity as it leads to duplication as all the
>> configuration stuff fits nicely).
> 
> If you can come up with a tasteful interface for doing this I wouldn't
> object but my suspicion is that it's going to be easier to reimplement.
> It does seem useful, I'm just worried about how the interface would
> look.
I'll have a think at some point and get back to you.
> 
>> As an aside, isn't your gather write more typically described
>> as a scatter write?  (writes one coherent set to a number of
>> disjoint locations?)
> 
> On the write side it's generally a gather (reading from different
> locations and writing out a continuous stream) while on the read side
> it's generally a scatter (reading a continuous data stream and writing
> it to multiple locations).  The gather here refers to getting data from
> more than one place and using it to transmit a single byte stream.
> 

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