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Re: [PATCH v3 0/8] dp8393x: fixes and improvements

From: Philippe Mathieu-Daudé
Subject: Re: [PATCH v3 0/8] dp8393x: fixes and improvements
Date: Sun, 11 Jul 2021 12:33:02 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

On 7/11/21 4:08 AM, Finn Thain wrote:
> On Sat, 10 Jul 2021, Philippe Mathieu-Daudé wrote:
>> The last 2 patches are included for Mark, but I don't plan to merge
>> them without Finn's Ack, and apparently they require more work.
> I tested the patch series both with and without the last 2 patches. Both 
> builds worked fine with my NetBSD/arc, Linux/mipsel and Linux/m68k guests.
> Tested-by: Finn Thain <fthain@linux-m68k.org>

Thank you very much :)

> I have no objection to patch 8/8 ("dp8393x: don't force 32-bit register 
> access"). I asked Mark to explain why it was a bug fix (since it didn't 
> change QEMU behaviour in my tests) but when I looked into it I found that 
> he is quite right, the patch does fix a theoretical bug.


> My only objection to patch 7/8 ("dp8393x: Rewrite dp8393x_get() / 
> dp8393x_put()") was that it could be churn.
> If I'm right that the big_endian flag should go away, commit b1600ff195 
> ("hw/mips/jazz: specify correct endian for dp8393x device") has already 
> taken mainline in the wrong direction and amounts to churn.

We might figure out with a BE guest image, the remove the endian flag.
I don't think the patch is worth removing, because it simplifies and
we'll only have to fix the endianess in 2 places, dp8393x_get/put. I
prefer to restrict the address space accesses there.

> I have the same reservations about patch 6/8 ("dp8393x: Store CRC using 
> device configured endianess"). Perhaps that should be NOTFORMERGE too 
> (even though it too a theoretical bug fix).

OK, dropped.

> Is there a good way to avoid using big_endian for storing the CRC and the 
> other DMA operations?

Could be, but I'd rather see this fixed generically in the MemoryRegion
API, not in this particular device model.

> BTW, if you see "sn0: receive buffers exhausted" occasionally logged by 
> the NetBSD 9.2 kernel, accompanied by packet loss, it's not a regression 
> in QEMU. I first observed it last year when stress testing dp8393x with 
> NetBSD 5.1. I believe this to be an old NetBSD sn driver bug because Linux 
> is unaffected.

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