[Skiboot] [PATCH 1/2] mowgli: Limit slot1 to Gen3 by default

[Frederic Barrat]

Hi,

Attached is a patch for you to try. You will also need to revert the 
previous patch (5262cdd1b99f77bca5951fc8132f9795ef0c2b87), since we no 
longer need the phb4_set_dt_max_link_speed() function.

   Fred


On 08/12/2020 12:50, Lulu_Su at wistron.com wrote:
> Hi Vasant,
> 
> Thank you for your reminder. I have a question for your opinion:
> Finally, there is a branch used by mowgli in ibm-op-release/op-build: release-mowgli,
> Maybe I can refer to the previous approach https://github.com/ibm-op-release/op-build/blob/release-mowgli/openpower/configs/mihawk_defconfig#L3 ,
> build a dedicated mowgli-patches, and add the modification of phb4_get_max_link_speed(), set max_link_speed to GEN3.
> What do you think?
> 
> 
> 
> Hi Frederic,
> 
> Thanks for your advice,
> I tried to make some modifications (attached files) and verified through EEH, the max-link-speed of this modification will not be lost,
> Do you have any suggestions for this modification?
> 
> But as you mentioned, there is an easier way to achieve this.
> I would like to ask how to set/add this property (ibm, max-link-speed) for PHB 0?
> 
> If there is any problem, please feel free to contact me.
> Thank you very much.
> 
> Best regards,
> Lulu Su
> 
> -----Original Message-----
> From: Vasant Hegde <hegdevasant at linux.vnet.ibm.com>
> Sent: Wednesday, December 2, 2020 3:04 PM
> To: Frederic Barrat <fbarrat at linux.ibm.com>; Lulu Su/WHQ/Wistron <Lulu_Su at wistron.com>; skiboot at lists.ozlabs.org; Stewart Smith <stewart at linux.vnet.ibm.com>
> Cc: Oliver OHalloran <oliveroh at au1.ibm.com>; skiboot-stable at lists.ozlabs.org; Klaus Heinrich Kiwi <klausk at br.ibm.com>
> Subject: Re: [Skiboot] [PATCH 1/2] mowgli: Limit slot1 to Gen3 by default
> 
> On 11/9/20 10:06 PM, Frederic Barrat wrote:
>>
>>
>> On 30/10/2020 03:22, Lulu Su wrote:
>>> From: LuluTHSu<Lulu_Su at wistron.com>
>>>
>>> Refer to the spec. of mowgli, limit the slot to Gen3 speed.
>>> For mowgli platform spec.
>>>
>>> Cc:skiboot-stable at lists.ozlabs.org
>>> Signed-off-by: LuluTHSu<Lulu_Su at wistron.com>
>>> ---
>>>    hw/phb4.c                 | 21 +++++++++++++++++++++
>>>    include/phb4.h            |  1 +
>>>    platforms/astbmc/mowgli.c | 16 ++++++++++++++++
>>>    3 files changed, 38 insertions(+)
>>>
>>> diff --git a/hw/phb4.c b/hw/phb4.c
>>> index 17a233f..de10bb0 100644
>>> --- a/hw/phb4.c
>>> +++ b/hw/phb4.c
>>> @@ -2991,6 +2991,27 @@ static unsigned int
>>> phb4_get_max_link_speed(struct phb4 *p, struct dt_node *np)
>>>        return max_link_speed;
>>>    }
>>> +/*
>>> + * Has the same effect as the ibm,max-link-speed property.
>>> + * i.e. sets the default link speed, while allowing NVRAM
>>> + * overrides, etc to still take effect.
>>> + */
>>> +void phb4_set_dt_max_link_speed(struct phb4 *p, int new_max) {
>>> +    uint64_t scr;
>>> +    int max;
>>> +
>>> +    /* take into account nvram settings, etc */
>>> +    if (pcie_max_link_speed)
>>> +        max = pcie_max_link_speed;
>>> +    else
>>> +        max = new_max;
>>> +
>>> +    scr = phb4_read_reg(p, PHB_PCIE_SCR);
>>> +    scr = SETFIELD(PHB_PCIE_SCR_MAXLINKSPEED, scr, max);
>>> +    phb4_write_reg(p, PHB_PCIE_SCR, scr); }
>>> +
>>
>>
>> This patch has already been merged, but I think there's a problem
>> here. This should work to limit the link speed at boot, when the link
>> is trained for the first time. However, since we're writing directly
>> in the register, skiboot won't memorize the limit and on the next link
>> reset/retrain (due to a EEH recovery or PCI hotplug for example), then
>> that is lost. And mowgli_setup_phb() won't be called either on that path.
> 
> 
> Lulu,
> 
> Can you guys fix this issue?
> 
> -Vasant
> 
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