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

[Lulu_Su at wistron.com]

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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