:: Re: [DNG] kernel drivers [WAS: How …
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Auteur: Enrico Weigelt, metux IT consult
Datum:  
Aan: dng
Onderwerp: Re: [DNG] kernel drivers [WAS: How long should I expect to wait for openrc to be ready in devuan ascii]
On 05.07.2017 23:30, Didier Kryn wrote:

> And there are a whole menagerie of addressing and transfer protocols,
> including chained dma transfers


Especially things like DMA are naturally kernel domain. I wouldn't ever
allow any direct access to dma controllers from userland.

> In our case it is waveform digitizers and the interaction is so >

complex that it cannot be done in a kernel module

What exactly is so complex about that ? Smells like a typical task
for IIO to me.

> Some others consider there should be one driver per VME device you
> want to talk to, on top of the raw VME driver.


Exactly.

> These people only ever had to deal with simplistic devices. Gabriel
> Paubert has never seen an application transfering more than a few bytes,
> while we are transferring data at 320MB/s.


Those kind of things usually involve proper timing, caring about
caching, etc, etc. Natural kernel domain.

>> Which absurdities, exactly ?
>      Bus errors were not reported to the application but instead caused 
> a message to syslog! This makes it hard to use; or your application 
> should monitor the log files!


Yes, that's hackish, of course.

>      This isn't the case here. AFAIU, their BSP contains a VME driver 
> and a device tree. I think it's all GPL. Their buzyness is to send 
> hardware and they make sure their clients can use it.


Looks like your vendor is an exception.

>      These are SBCs with everything soldered: VME, flash memory, UARTs, 
> USB hub, Sata controllers, Ethernet ports etc... And you just plug it 
> into a VME crate. It makes no sense to develop a board like this to use 
> a dozen of them. We made the digitizers and it was already a big deal 
> for our small team.

>
>      Could you develop what is IIO for DAQ devices? 


What's the difference between you digitizes and usual DAQ devices ?
What do you actually do with them ?

Some clear requirements on the table, please ;-)

> Is it something allowing to write drivers in user space?


What kind of drivers do you wanna have in userland ? And why ?


--mtx