[U-Boot] [PATCH 2/2] net: add driver for Synopsys Ethernet QoS device

[Joe Hershberger]

On Fri, Oct 14, 2016 at 1:35 AM, Stephen Warren <swarren at wwwdotorg.org> wrote:
> On 10/11/2016 04:48 PM, Joe Hershberger wrote:
>>
>> On Tue, Oct 4, 2016 at 12:13 AM, Stephen Warren <swarren at wwwdotorg.org>
>> wrote:
>>>
>>> On 09/23/2016 03:49 PM, Joe Hershberger wrote:
>>>>
>>>>
>>>> Hi Stephen,
>>>>
>>>> Thanks for sending this! I have some comments below.
>>>>
>>>> Cheers,
>>>> -Joe
>>>>
>>>> On Mon, Sep 12, 2016 at 12:48 PM, Stephen Warren <swarren at wwwdotorg.org>
>>>> wrote:
>>>>>
>>>>>
>>>>> From: Stephen Warren <swarren at nvidia.com>
>>>>>
>>>>> This driver supports the Synopsys Designware Ethernet QoS (Quality of
>>>>> Service) a/k/a eqos IP block, which is a different design than the HW
>>>>> supported by the existing designware.c driver. The IP supports many
>>>>> options for bus type, clocking/reset structure, and feature list. This
>>>>> driver currently supports the specific configuration used in NVIDIA's
>>>>> Tegra186 chip, but should be extensible to other combinations quite
>>>>> easily, as explained in the source.
>>>
>>>
>>>>> diff --git a/drivers/net/dwc_eth_qos.c b/drivers/net/dwc_eth_qos.c
>>>
>>>
>>>> +static int eqos_start(struct udevice *dev)
>>>
>>>
>>>>> +       /* Update the MAC address */
>>>>> +       val = (plat->enetaddr[5] << 8) |
>>>>> +               (plat->enetaddr[4]);
>>>>> +       writel(val, eqos->regs + EQOS_MAC_ADDRESS0_HIGH);
>>>>> +       val = (plat->enetaddr[3] << 24) |
>>>>> +               (plat->enetaddr[2] << 16) |
>>>>> +               (plat->enetaddr[1] << 8) |
>>>>> +               (plat->enetaddr[0]);
>>>>> +       writel(val, eqos->regs + EQOS_MAC_ADDRESS0_LOW);
>>>>
>>>>
>>>>
>>>> This should be implemented in write_hwaddr() op.
>>>
>>>
>>> That op is never called because this driver is only instantiated by
>>> device
>>> tree. Since this code can't be skipped, it can't be moved to that op.
>>
>>
>> I don't understand what you're saying here. That op is called in
>> eth_initialize() on every device found in device tree.
>
>
> Oh, so it is. I must have screwed up my tracing before.
>
> Anyway, I still don't believe using write_hwaddr() is correct for this HW.
> It's marked optional in include/net.h; it would be implemented in cases
> where the MAC address should be passed to subsequent SW in Ethernet
> controller registers. That's not the case here. The master location for the
> MAC address is in an unrelated EEPROM that all drivers must read.

That sounds more like a NV storage location for a read_rom_hwaddr() op
to get a default mac addr that can be overridden with the env. The
write_hwaddr is about what the mac uses to filter for limiting packet
ingress. One reason to support it as an op is so that when the env var
for the mac address is changed, the mac filter in the hw is also
updated.

> Resetting
> the device (as any driver would do to guarantee correct operation no matter
> what SW ran before), or never initializing it in the first place (as is the
> case now without any driver in U-Boot) means that those registers cannot be
> assumed to contain valid data.

That's what the comment I quoted in my last mail is directly
addressing. It does make that data valid.

> Thus SW after U-Boot won't rely on the MAC
> address register values,

And yet it does in most cases, hence the comment I quoted in the last mail.

> and hence there's no need to implement
> .write_hwaddr() separately, since that's the only reason it exists
> separately according to the comments in include/net.h.