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Re: [Qemu-devel] [PATCH 08/17] imx_fec: Add support for multiple Tx DMA


From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH 08/17] imx_fec: Add support for multiple Tx DMA rings
Date: Mon, 9 Oct 2017 18:06:00 +0100

On 9 October 2017 at 16:38, Andrey Smirnov <address@hidden> wrote:
> On Fri, Oct 6, 2017 at 7:10 AM, Peter Maydell <address@hidden> wrote:
>> On 18 September 2017 at 20:50, Andrey Smirnov <address@hidden> wrote:
>>> More recent version of the IP block support more than one Tx DMA ring,
>>> so add the code implementing that feature.
>>>
>>> Cc: Peter Maydell <address@hidden>
>>> Cc: Jason Wang <address@hidden>
>>> Cc: address@hidden
>>> Cc: address@hidden
>>> Cc: address@hidden
>>> Signed-off-by: Andrey Smirnov <address@hidden>
>>
>> I'm surprised this doesn't mean "we have a property on the device
>> to indicate what IP version it is, which the boards set". Or are
>> all our current boards mismodelling their ethernet devices with the
>> wrong number of TX rings ?
>>
>
> As far as I know the only already emulated SoC that this affects is
> i.MX6, and, no, it doesn't mismodel its Ethernet device since it has
> version of the IP block with only one Tx ring. I didn't add any notion
> of versioning because it didn't seem necessary, since 3-ring IP block
> should be backwards compatible with 1-ring version and host drivers
> written for the latter will end up using only ring #1 of the 3-ring
> block.

It is guest visible if the guest looks for it, though, so I think
we should have a device property to set the number of Tx rings
(or to set the version number of the IP if that's in a guest
visible register and a more useful way to model it) so we can
get it right for both boards.

thanks
-- PMM



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