[PATCH v12 1/4] PHY: Add function set_speed to generic PHY framework

[Loc Ho]

Hi Felipe and Kishon,

>>> >> >> This patch adds function set_speed to the generic PHY framework operation
>>> >> >> structure. This function can be called to instruct the PHY underlying layer
>>> >> >> at specified lane to configure for specified speed in hertz.
>>> >> >
>>> >> > why ? looks like clk_set_rate() is your friend here. Can you be more
>>> >> > descriptive of the use case ? When will this be used ?
>>> >> >
>>> >>
>>> >> The phy_set_speed is used to configure the operation speed of the PHY
>>> >> at run-time. The clock interface in general is used to configure the
>>> >> clock input to the IP. I don't believe they are the same thing. Maybe
>>> >> it will be clear in my response to your second email
>>> >
>>> > The problem with this is that you end up adding SATA-specific details to
>>> > something which is supposed to be generic.
>>>
>>> Setting the operation speed is pretty generic from an interface point
>>> of view. An generic multi-purpose PHY can support multiple speed. If
>>
>> no it's not. Specially when you consider that your "speed" argument can
>> be just about anything and depending on the underlying bus, it *will* be
>> treated differently. Note that e.g. in OMAP devices the exact *same* PHY
>> IP is used for PCIe, SATA and USB... now, let's assume for the sake of
>> argument that we were to implement ->set_speed() in that environment,
>> how do you plan to do that ? a 6MHz arguments isn't valid from USB stand
>> point and could mean different things in PCIe or SATA.
>>
>
> Correct me if I am wrong here. If the same PHY is used for PCIe, SATA,
> and USB, would you not need to indicate what speed the PHY should be
> operated at - unless the underlying IP magically negotiate and
> configured automatically? If so, what about PHY isn't so intelligent?
> How should you suggest that we handle these?
>
>>> the upper layer wish to operate at an specified speed (say for testing
>>> purpose and etc), it can be allowed.
>>
>> anything for testing purposes, should be limited to test scenarios.
>
> Testing purpose is only one use case. Another use case is to limit the
> speed so that I can confirm the driver actually works with various
> speed of the device and handle correctly.
>
>>
>>> > After negoatiation, don't you
>>> > get any interrupt from your PHY indicating that link speed negotiation
>>> > is done ? Or is that IRQ only on AHCI IP ?
>>>
>>> There is NO interrupt from the PHY. The IRQ is assoicated with the
>>> AHCI IP. With SATA host flow, it starts off with an COMRESET to start
>>> the link negotiation. At that point, it will poll for completion.
>>>
>>> Any other concerns?
>>
>> hey, calm down... just trying to prevent us from applying something
>> which isn't truly generic and I don't think "->set_speed" is generic
>> enough. The semantics of the "speed" argument won't be valid for all use
>> cases.
>>
>> I can already see people using that to pass
>> USB_SPEED_{LOW,FULL,HIGH,SUPER}, instead of actual speed numbers. We wil
>> end up with a mess to handle from a PHY driver, specially in cases such
>> as OMAP where, as mentioned above, the same IP is used for SATA, PCIe
>> and USB3.
>>
>
> This PHY isn't as "intelligent" as other PHY's. What would you suggest
> as I need an method to indicate to the underlying PHY that I want to
> operate at an specified speed?

Sorry if I am pinging you guys too fast here. I am look from an
solution and open to any solution in which it is acceptable for your
original intent of the generic PHY framework. I understand that you
don't believe set_speed is generic enough and may not apply to omap.
Or if you prefer we can try changing the init function to take an
initial MAX speed?

-Loc