* PMBus and SMBUS_BLOCK with "extended" lenght
@ 2017-03-31 8:17 Benjamin Herrenschmidt
2017-03-31 16:33 ` Wolfram Sang
0 siblings, 1 reply; 4+ messages in thread
From: Benjamin Herrenschmidt @ 2017-03-31 8:17 UTC (permalink / raw)
To: linux-i2c
Hi folks !
Did anybody give thoughts to how we could support "smbus" block
transfers with a size up to 0xff ? This is an extension of smbus
that part of the PMbus protocol spec.
Our current code has a lot of places where I2C_SMBUS_BLOCK_MAX is
hard wired. Including down in almost all drivers.
So it would have to be an evolutionary process.
I was thinking a message flag along with a functionality bit
maybe ?
Cheers,
Ben.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: PMBus and SMBUS_BLOCK with "extended" lenght
2017-03-31 8:17 PMBus and SMBUS_BLOCK with "extended" lenght Benjamin Herrenschmidt
@ 2017-03-31 16:33 ` Wolfram Sang
2017-04-19 5:40 ` Benjamin Herrenschmidt
0 siblings, 1 reply; 4+ messages in thread
From: Wolfram Sang @ 2017-03-31 16:33 UTC (permalink / raw)
To: Benjamin Herrenschmidt; +Cc: linux-i2c
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Hi,
> Did anybody give thoughts to how we could support "smbus" block
> transfers with a size up to 0xff ? This is an extension of smbus
> that part of the PMbus protocol spec.
For completeness, SMBus Spec V3 (released 2015) increased the allowed
transfer size to 255 as well.
>
> Our current code has a lot of places where I2C_SMBUS_BLOCK_MAX is
> hard wired. Including down in almost all drivers.
>
> So it would have to be an evolutionary process.
>
> I was thinking a message flag along with a functionality bit
> maybe ?
I have never really scratched my head about this issue yet and don't
know of any on-going activity. It is notable, though, that we export
I2C_SMBUS_BLOCK_MAX to userspace, too.
Regards,
Wolfram
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: PMBus and SMBUS_BLOCK with "extended" lenght
2017-03-31 16:33 ` Wolfram Sang
@ 2017-04-19 5:40 ` Benjamin Herrenschmidt
2017-04-19 6:54 ` Wolfram Sang
0 siblings, 1 reply; 4+ messages in thread
From: Benjamin Herrenschmidt @ 2017-04-19 5:40 UTC (permalink / raw)
To: Wolfram Sang; +Cc: linux-i2c
On Fri, 2017-03-31 at 18:33 +0200, Wolfram Sang wrote:
> Hi,
>
> > Did anybody give thoughts to how we could support "smbus" block
> > transfers with a size up to 0xff ? This is an extension of smbus
> > that part of the PMbus protocol spec.
>
> For completeness, SMBus Spec V3 (released 2015) increased the allowed
> transfer size to 255 as well.
>
> >
> > Our current code has a lot of places where I2C_SMBUS_BLOCK_MAX is
> > hard wired. Including down in almost all drivers.
> >
> > So it would have to be an evolutionary process.
> >
> > I was thinking a message flag along with a functionality bit
> > maybe ?
>
> I have never really scratched my head about this issue yet and don't
> know of any on-going activity. It is notable, though, that we export
> I2C_SMBUS_BLOCK_MAX to userspace, too.
Right. I don't think we can change it. We could either define a whole
new set of block read/write that support "extended" max, or probably
easier, a msg flag indicating that this is supported.
We would need a backend bus capability as well since all the busses
today will barf if the device returns something larger than
I2C_SMBUS_BLOCK_MAX.
Not a huge deal, all this is just a thought, I don't think I have a
device to deal with today that will return more on any of my systems (I
can double check later). I just noticed that while reading the PMbus
spec.
Cheers,
Ben.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: PMBus and SMBUS_BLOCK with "extended" lenght
2017-04-19 5:40 ` Benjamin Herrenschmidt
@ 2017-04-19 6:54 ` Wolfram Sang
0 siblings, 0 replies; 4+ messages in thread
From: Wolfram Sang @ 2017-04-19 6:54 UTC (permalink / raw)
To: Benjamin Herrenschmidt; +Cc: linux-i2c
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> Not a huge deal, all this is just a thought, I don't think I have a
> device to deal with today that will return more on any of my systems (I
> can double check later). I just noticed that while reading the PMbus
> spec.
I once stumbled over a TPM device which had a flag to send either 32 or
255 byte. Can't recall which exactly, though.
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^ permalink raw reply [flat|nested] 4+ messages in thread
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2017-03-31 8:17 PMBus and SMBUS_BLOCK with "extended" lenght Benjamin Herrenschmidt
2017-03-31 16:33 ` Wolfram Sang
2017-04-19 5:40 ` Benjamin Herrenschmidt
2017-04-19 6:54 ` Wolfram Sang
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