How to replace control code in gdm72xx?

How to replace control code in gdm72xx?

[Michalis Pappas]

Hi,

I'm currently working on bringing the gdm72xx WiMAX driver out of
staging. The driver currently uses two control channels:

1. The SIOCDEVPRIVATE ioctl to send and receive state messages

2. A customly defined netlink protocol for passing messages verbatim to
the device controller

AFAIK both of the above are deprecated, so I considered switching to
the interface defined in wimax.h, which defines a communication protocol
over generic netlink that replaces (2) nicely. However it is not
compatible with (1), as:

* Except from the device status, the gdm72xx driver uses two more types
of messages (connection and OMA status), which is not supported
by wimax.h.

* The gdm driver needs to be able to receive status messages from
userspace, which is not supported by wimax.h either.

I therefore consider using the wimax stack as defined in wimax.h for the
netlink part, but replacing the ioctl with a file under /sys/class/net/wm0/

My questions are whether the above location would be the right place for
that file, and, more importantly, whether this is a generally a valid
approach and not just an ugly workaround.

Thanks,

Michalis
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Re: How to replace control code in gdm72xx?

[Greg KH]

On Wed, Jul 16, 2014 at 09:24:28PM +0100, Michalis Pappas wrote:
> Hi,
> 
> I'm currently working on bringing the gdm72xx WiMAX driver out of
> staging. The driver currently uses two control channels:
> 
> 1. The SIOCDEVPRIVATE ioctl to send and receive state messages
> 
> 2. A customly defined netlink protocol for passing messages verbatim to
> the device controller
> 
> AFAIK both of the above are deprecated, so I considered switching to
> the interface defined in wimax.h, which defines a communication protocol
> over generic netlink that replaces (2) nicely. However it is not
> compatible with (1), as:
> 
> * Except from the device status, the gdm72xx driver uses two more types
> of messages (connection and OMA status), which is not supported
> by wimax.h.
> 
> * The gdm driver needs to be able to receive status messages from
> userspace, which is not supported by wimax.h either.

What type of status messages are needed to be sent to the driver?

> I therefore consider using the wimax stack as defined in wimax.h for the
> netlink part, but replacing the ioctl with a file under /sys/class/net/wm0/

Is anyone still working on wimax to even object to add new functions
like this?  :)

thanks,

greg k-h

Re: How to replace control code in gdm72xx?

[Ben Chan]

On Wed, Jul 16, 2014 at 1:40 PM, Greg KH <greg@kroah.com> wrote:
>
> On Wed, Jul 16, 2014 at 09:24:28PM +0100, Michalis Pappas wrote:
> > Hi,
> >
> > I'm currently working on bringing the gdm72xx WiMAX driver out of
> > staging. The driver currently uses two control channels:
> >
> > 1. The SIOCDEVPRIVATE ioctl to send and receive state messages
> >
> > 2. A customly defined netlink protocol for passing messages verbatim to
> > the device controller
> >
> > AFAIK both of the above are deprecated, so I considered switching to
> > the interface defined in wimax.h, which defines a communication protocol
> > over generic netlink that replaces (2) nicely. However it is not
> > compatible with (1), as:
> >
> > * Except from the device status, the gdm72xx driver uses two more types
> > of messages (connection and OMA status), which is not supported
> > by wimax.h.
> >
> > * The gdm driver needs to be able to receive status messages from
> > userspace, which is not supported by wimax.h either.
>
> What type of status messages are needed to be sent to the driver?
>

>From what I read from the user-space code, the custom ioctl is to read
the following information from the driver:

enum {
    SIOC_DATA_FSM,           // Device/Connection State
    SIOC_DATA_NETLIST,       // Network list
    SIOC_DATA_CONNNSP,     // Connected NSP
    SIOC_DATA_CONNCOMP,    // Connection completion info
    SIOC_DATA_PROFILEID,    // WiMAX profile ID
    SIOC_DATA_END
};

Reference:

https://chromium.googlesource.com/chromiumos/third_party/gdmwimax/+/master/sdk/io.c
https://chromium.googlesource.com/chromiumos/third_party/gdmwimax/+/master/sdk/sdk.c
https://chromium.googlesource.com/chromiumos/third_party/gdmwimax/+/master/sdk/wm_ioctl.h


>
> > I therefore consider using the wimax stack as defined in wimax.h for the
> > netlink part, but replacing the ioctl with a file under /sys/class/net/wm0/
>
> Is anyone still working on wimax to even object to add new functions
> like this?  :)
>

The driver has a corresponding user-space library, so I'd like to
figure out a way to maintain backward compatibility if possible. But
I'm happy to help make minor changes to  the user-space library in
case we need to modify the ioctl / netlink part of the driver (caveat:
I'm not the author of the driver or the user-space library).

> thanks,
>
> greg k-h
> _______________________________________________
> devel mailing list
> devel@linuxdriverproject.org
> http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel

Re: How to replace control code in gdm72xx?

[Michalis Pappas]

On 07/17/2014 01:59 AM, Ben Chan wrote:
> 
> From what I read from the user-space code, the custom ioctl is to read
> the following information from the driver:
> 
> enum {
>     SIOC_DATA_FSM,           // Device/Connection State
>     SIOC_DATA_NETLIST,       // Network list
>     SIOC_DATA_CONNNSP,     // Connected NSP
>     SIOC_DATA_CONNCOMP,    // Connection completion info
>     SIOC_DATA_PROFILEID,    // WiMAX profile ID
>     SIOC_DATA_END
> };
> 

Sorry for the late reply, I was away. 

I had a look at the library's source to clear things out a bit. From what I see the driver is tightly coupled -actually dependent- to the library, as all control operations are performed by the latter. So without the library, the driver is pretty much of no use.

The way control works is that the driver acts as a middleman between the library and the hci. All operations are initiated and handled by the library, through the netlink channel. So the information mentioned above, eg SIOC_DATA_NETLIST, are requested by the library, by sending the appropriate command to the driver via netlink. The driver will forward the request to the hci and forward the response back to userspace.

Here is where the ioctl part interface into play. The ioctl interface supports two commands: SIOCS_DATA and SIOCG_DATA (set data / get data). The above can store and retrieve data from the driver, which in turn keeps this information in the nic.sdk_data array. This array maintains one element for each one of the SIOC_DATA_* mentioned above.

So once received and processed, the library will store the received data (eg the network list) in the driver's memory via the ioctl, just to retrieve it again later(!) With the exception of SIOC_FSM_XXX, the driver does not inspect or process the contents of these objects by any means (see gdm_wimax_ioctl() in gdm_wimax.c).

Now, I have no clue why it was written this way, but as per its current 
status all this might as well (and probably should) be stored locally, in userspace memory. So the ioctl part can be completely removed, and the driver will then be in conformance with the interface defined by the wimax stack, in wimax.h.

> 
> The driver has a corresponding user-space library, so I'd like to
> figure out a way to maintain backward compatibility if possible. But
> I'm happy to help make minor changes to  the user-space library in
> case we need to modify the ioctl / netlink part of the driver (caveat:
> I'm not the author of the driver or the user-space library).
> 

Why maintain backwards compatibility? The only part to change is the
communication layer between the library and the driver. The applications
using the library won't notice any difference.

IMO the right thing to do is to push whatever changes made to the library upstream. Which brings us to the question of who is the library's maintainer and where is it officially hosted?

If the answers to the above are "none" and "nowhere", then we have a bigger problem, as the updated driver will appear to be broken to anyone who hasn't been updated with the latest version of the library.

In conclusion, I am happy to fix the driver and even write a patch for the corresponding userspace parts, but only as long as:

* You are willing to help me with testing, as I do not own the hardware.

* My work will not be waisted. What I mean by that is, if the library has been distributed only to a few parties worldwide, then IMO we'd better delete the driver and let it be distributed along with the library, since they are interdependent anyway.

In any other case, I'd rather move on to some other driver that does not depend on third party stuff :)

Thanks,

Michalis