linux-kernel - Re: [net-next 1/2] net: ethernet: slicoss: add slicoss gigabit ethernet driver

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Date:   Tue, 15 Nov 2016 23:54:43 +0100
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>
Cc:     davem@...emloft.net, charrer@...critech.com, liodot@...il.com,
        gregkh@...uxfoundation.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [net-next 1/2] net: ethernet: slicoss: add slicoss gigabit
 ethernet driver

On 15.11.2016 23:39, Florian Fainelli wrote:
> On 11/15/2016 02:34 PM, Lino Sanfilippo wrote:
>> On 15.11.2016 22:59, Andrew Lunn wrote:
>>>> The link state is retrieved by a command to the application processor that is running 
>>>> on the network card. Also the register to set the phy configuration is write-only, so
>>>> it is not even possible to do the usual mdio bit-banging in the Phy read() and write()
>>>> functions (however there seems to be another application processor command reserved 
>>>> for retrieving the PHY settings, but I have not tried it yet). 
>>>
>>>>> +  			val = MII_BMCR << 16 | SLIC_PCR_AUTONEG |
>>>>> +		     	         SLIC_PCR_AUTONEG_RST;
>>>>> +			slic_write(sdev, SLIC_REG_WPHY, val);
>>>
>>> This actually looks a lot like an MDIO write operation. The upper 16
>>> bits are the register, and the lower 16 bits are the data. What you
>>> don't have is the address. But maybe it is limited to one address.
>>>
>>> If the processor command reserved for read works in a similar way, you
>>> have enough to do an MDIO bus.
>>>
>> 
>> Ok, I will give it a try. Reading values via the application processor
>> is a bit awkward though, since it requires an address to a dma area as part of
>> the command and then the AP informs the driver via irq that the dma memory has 
>> been written. So probably the irq handler will have to set some flag and
>> the mdio_read() function will have to poll for that flag in place of doing 
>> bit-banging a register. 
> 
> That's a bit unusual compared to typical controllers that are usually
> memory-mapped and that you can either write to, read/poll to know about
> completion. I suppose that you could still have a mdiobus implementation
> that is able to read to/from PHYs by submitting a command to the AP,
> wait on a completion structure, and have the interrupt handler do the
> completion of the command?
> 

Thats essentially what I meant by setting a flag in the irq handler. The mdio
function would have to check somehow if the irq has been fired (be it by means
of a flag or a completion that is set by the irq handler and checked by the 
mdio function). So I agree that it should work (if reading via the AP command
is actually possible).

Lino