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Re: [Qemu-devel] [PATCH v2 1/4] Add i.MX FEC Ethernet driver

From: Jean-Christophe DUBOIS
Subject: Re: [Qemu-devel] [PATCH v2 1/4] Add i.MX FEC Ethernet driver
Date: Sun, 05 May 2013 16:05:05 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130404 Thunderbird/17.0.5

On 05/05/2013 03:31 PM, Andreas Färber wrote:
Am 05.05.2013 15:14, schrieb Jean-Christophe DUBOIS:
On 05/05/2013 05:11 AM, Peter Crosthwaite wrote:
Hi JC,

On Sun, May 5, 2013 at 12:09 AM, Jean-Christophe DUBOIS
<address@hidden>  wrote:
This is based on the mcf_fec.c FEC implementation for ColdFire.
Note that ColdFire is one of the least maintained targets in QEMU...

Well, that's too bad.

I actually believe the ColdFire FEC implementation would not work in actual QEMU (but I don't plan to build a ColdFire Kernel and RootFS to find out).

+static int imx_fec_can_receive(NetClientState *nc)
+    imx_fec_state *s = qemu_get_nic_opaque(nc);
Andreas, do we care about QOM casts coming from random void* opaques?
Generally no. If we ever switch to C++ or some other OO language we'll
have to touch casts anyway.

Peter, please note that I usually don't have time to read through all
patches - noticed this inline question incidentally only.

OK, I am going to do a QOM cast anyway.
You should check how frequently this function is called - the current
OBJECT_CHECK() implementation does at least one string comparison, so
I'd suggest to avoid it here. That is, if the type passed in as opaque
matches the type assigned here (thinking of interfaces).

Hum, ... you are going to be unhappy with my new patch.

+    return s->rx_enabled;

Not knowing this piece of hardware, might it make sense to call it
"imx-fec" when there's another FEC for ColdFire?

I am calling it "imx.fec" in the new version of the file (to be equivalent to "imx.i2c" I did for I2C).

  Or are they the same
thing and should be unified?
Well, they are certainly very similar but are different on a few points. In particular the "buffer descriptors" are reversed between i.MX and Coldfire. Linux does a compile time decision about these buffer descriptors but I don't know how this would work with Qemu (can you make a different compile time decision for 2 different targets?).

We could also implement a more cumbersome run time decision but I wanted to keep simple.

And anyway I don't have Coldfire (cross compilers, rootfs, ...) setup around to test.


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