> > > This patch adds two new members to the
> mtd_partition structure,
> > > a function handler which will be
> > > called during setup of the
> > > partition and an argument to be passed to this
> setup function.
> >
> > Ick.
> >
> > I don't mind providing the mtd_macc_{read,write}
> helper functions,
> > although they should work on generic MTD
> > >devices not just on partitions.
> > But do we really have to do the callout to
> > arbitrary functions from
> > _within_ the core MTD code... why can't we
> > do that in the board driver?
I think the short answer is that the callout is
what provides the board drivers enough information
to make the correct calls.
On Wed, 2010-07-07 at 04:08 -0700, David Brownell wrote:
>
> I think the short answer is that the callout is
> what provides the board drivers enough information
> to make the correct calls.
I don't see how.
The only information it passes to the callout is the information it was
already *given* in the partition structure.
I'm more inclined to believe Sudhakar's claim that you'll get an
'initialization sequence problem', although I'm not sure I believe it
can't be solved in a better way than this.
I'm also unhappy that it only works on partitioned devices -- that seems
wrong.
--
David Woodhouse Open Source Technology Centre
[email protected] Intel Corporation
--- On Wed, 8/4/10, David Woodhouse <[email protected]> wrote:
> On Wed, 2010-07-07 at 04:08 -0700,
> David Brownell wrote:
> >
> > I think the short answer is that the callout is
> > what provides the board drivers enough information
> > to make the correct calls.
EMPHASIS ON "CORRECT" ...
> I don't see how.
>
> The only information it passes to the callout is the
> information it was
> already *given* in the partition structure.
There can be multiple such structures, each
of which describes different data to be extracted
from different persistent media contexts.
Examples: one context holds one MAC address (and
another, a different one) ... another might embed
calibration data; another, serial numbers; etc.
Pass the wrong context around, you've trashed all
the data instead of getting it right.
> I'm more inclined to believe Sudhakar's claim that you'll
> get an
> 'initialization sequence problem', although I'm not sure I
> believe it
> can't be solved in a better way than this.
"Initialization sequence" is a grab-bag category
that covers most init issues.
Point is to ensure that enough of the right context
information is available to initialize correctly.
So the right data is extracted and passed on.
>
> I'm also unhappy that it only works on partitioned devices
> -- that seems wrong.
Very different issue. Seems easily fixable
if needed. Agreed that e.g. EEPROMS won't
often be partitioned (unlike flash).
On Wed, 2010-08-04 at 03:31 -0700, David Brownell wrote:
> Point is to ensure that enough of the right context
> information is available to initialize correctly.
> So the right data is extracted and passed on.
Forgive me if I'm being dim (and in particular, please forgive me if I'm
going over something that was already discussed; I know it's been a
while). But I don't see why it needs to be passed through the core MTD
code.
To take the simple case of an unpartitioned MTD device -- why can't the
map driver (or whatever) just call the maccessor setup function for
itself, directly, right after calling add_mtd_device() with its
newly-probed MTD device?
And for partitions, why can't it do the same, on the appropriate
partition.
OK, the answer to the latter question is that you don't actually *have*
the pointers to each partition you register. But that's easily fixed.
If we make add_mtd_partitions() take an extra 'struct mtd_info **'
argument and put pointers to the slave mtd 'devices' into that, it means
that your board driver *can* reliably get the mtd pointer for the fourth
partition, or whatever it needs. And can then just do the memory
accessor setup for itself.
Isn't that enough?
--
David Woodhouse Open Source Technology Centre
[email protected] Intel Corporation
--- On Wed, 8/4/10, David Woodhouse <[email protected]> wrote:
> > Point is to ensure that enough of the right context
> > information is available to initialize correctly.
> > So the right data is extracted and passed on.
And also, ISTR, that the mechanism is general
enough to work with both MTD and EEPROM ...
>
> Forgive me if I'm being dim (and in particular, please
> forgive me if I'm
> going over something that was already discussed; I know
> it's been a
> while).
I also am at risk of getting lost in a pile
of hypotheticals which have been left behind
earlier in these threads.
But I don't see why it needs to be passed through
> the core MTD code.
>
> To take the simple case of an unpartitioned MTD device --
> why can't the
> map driver (or whatever) just call the maccessor setup
> function for
> itself, directly, right after calling add_mtd_device() with
> its newly-probed MTD device?
No idea, except that doing it once rather than
modifying every driver would seem healthier.
Surely changing all drivers is a Bad Thing.
>
> And for partitions, why can't it do the same, on the
> appropriate partition.
>
> OK, the answer to the latter question is that you don't
> actually *have*
> the pointers to each partition you register. But that's
> easily fixed.
>
> If we make add_mtd_partitions() take an extra 'struct
> mtd_info **'
> argument and put pointers to the slave mtd 'devices' into
> that, it means
> that your board driver *can* reliably get the mtd pointer
> for the fourth
> partition, or whatever it needs. And can then just do the
> memory
> accessor setup for itself.
>
> Isn't that enough?
Might be. Not my patch though... You asked why
the context was needed along with the partition
data (otherwise not available); I answered.
Still haven't seen a better patch though.