Re: [PATCH net-next v4 1/2] dts: Add a binding for Synopsys emac max-frame-size

On Thu, Jan 16, 2014 at 11:50 AM, Ben Hutchings
[off-list ref] wrote:

On Thu, 2014-01-16 at 08:05 -0600, Vince Bridgers wrote:

quoted

This change adds a parameter for the Synopsys 10/100/1000
stmmac Ethernet driver to configure the maximum frame
size supported by the EMAC driver. Synopsys allows the FIFO
sizes to be configured when the cores are built for a particular
device, but do not provide a way for the driver to read
information from the device about the maximum MTU size
supported as limited by the device's FIFO size.

Signed-off-by: Vince Bridgers <redacted>
---
V4: add comments to explain use of max-frame-size with respect
    to inconsistent definition and use in the ePAPR v1.1 spec

Well, ePAPR does not seem to be consistent with itself. :-)

quoted

V3: change snps,max-frame-size to max-frame-size
V2: change snps,max-mtu to snps,max-frame-size
---
 Documentation/devicetree/bindings/net/stmmac.txt |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/net/stmmac.txt b/Documentation/devicetree/bindings/net/stmmac.txt
index eba0e5e..d553be2 100644
--- a/Documentation/devicetree/bindings/net/stmmac.txt
+++ b/Documentation/devicetree/bindings/net/stmmac.txt

@@ -29,7 +29,17 @@ Required properties:
                              ignored if force_thresh_dma_mode is set.

 Optional properties:
-- mac-address: 6 bytes, mac address
+- mac-address:               6 bytes, mac address
+- max-frame-size:    Maximum frame size permitted. This parameter is useful
+                     since different implementations of the Synopsys MAC may
+                     have different FIFO sizes depending on the selections
+                     made in Synopsys Core Consultant. Note that the usage
+                     is inconsistent with the definition in the ePAPR v1.1
+                     specification, as it defines max-frame-size inclusive
+                     of the MAC DA, SA, Ethertype and CRC while usage is
+                     consistent with the IEEE definition of MAC Client
+                     Data, which is sans the MAC DA, SA, Ethertype and
+                     CRC.

[...]

While this is very precise, I fear that it is now so verbose that it
actually becomes confusing.  Can this not be condensed to 'the maximum
MTU and MRU, rather than the maximum Ethernet frame size'?

Ben.

Sure, I'll cut this down and resubmit as V5. How about

"The Maximum Transfer Unit (IEEE defined MTU), rather than the maximum
frame size."

Cheers,

Vince