linux-kernel - Re: [RFC PATCH v6 3/3] drivers: nvmem: Add Vybrid OCOTP support

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Date:	Fri, 10 Jul 2015 23:39:46 +0530
From:	maitysanchayan@...il.com
To:	Stefan Wahren <stefan.wahren@...e.com>
Cc:	stefan@...er.ch, srinivas.kandagatla@...aro.org,
	kernel@...gutronix.de, linux-kernel@...r.kernel.org,
	shawn.guo@...aro.org, maxime.ripard@...e-electrons.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH v6 3/3] drivers: nvmem: Add Vybrid OCOTP support

Hello Stefan,

On 15-07-08 22:55:23, Stefan Wahren wrote:
> Hi Sanchayan,
> 
> > maitysanchayan@...il.com hat am 8. Juli 2015 um 07:39 geschrieben:
> >
> >
> > [...]
> > > > >
> > > > > Looking at valid_fuse_addr shows me 0x3F as last valid register. So the
> > > > > rest
> > > > > of the buffer ( 0xD00 - sizeof(valid_fuse_addr) ) in case of raw access
> > > > > could be
> > > > > uninitializied.
> > > >
> > > > Sorry I did not exactly get you here. The intention behind using the
> > > > valid_fuse_addr
> > > > is to allow reading only from valid fuse addresses and avoid reading from
> > > > all
> > > > other
> > > > locations as per the Fuse map address table 35-1.
> > >
> > > Yes, i got your intention. But from my unterstand the read function should
> > > fill
> > > up
> > > the complete buffer with defined values. My MXS OCOTP driver have the same
> > > problem
> > > and fill up the invalid registers with zero.
> >
> > I must admit I had not thought of that. Thats a valid point. I dont know at
> > the
> > moment however what would be the correct approach here. Perhaps filling
> > locations
> > other than the valid fuse addresses as per the fuse map table with 0xBADABADA
> > is
> > the right thing? Anyways that's what is going to be returned if we were to
> > read
> > a location which is read locked or reserved.
> 
> since we are operating in userspace the behavior shouldn't be specific to the
> device.
> It would be good when all drivers behave the same. But i think it would be much
> better
> as the nvmem framework take care of it and preinit the buffer with a defined
> value.

There is a v7 now. Yet to give that a try or look at it.

> 
> >
> > However since the fuse address and base address mapping is not exactly linear,
> > this would require some additional logic than the simple thing I did. 
> 
> I defined a regmap_access_table for valid read registers in my case. But i think
> in your case
> an implementation of the readable_reg callback in the regmap_config would be
> more elegant.
> 
> You can validate your implementation under /sys/kernel/debug/regmap/

Thank you for the input. I will have a look at it and give it a try.

> 
> Sorry, i'm a newbie to regmap.

Same here as well :)

Regards,
Sanchayan.
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