linux-kernel - Re: [PATCH 00/10] Add PCIe Bandwidth Controller

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Date:   Mon, 11 Sep 2023 18:51:10 +0530
From:   Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
CC:     <linux-pci@...r.kernel.org>, Bjorn Helgaas <helgaas@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Lukas Wunner <lukas@...ner.de>,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Alex Deucher <alexdeucher@...il.com>
Subject: Re: [PATCH 00/10] Add PCIe Bandwidth Controller


On 9/4/2023 4:46 PM, Ilpo Järvinen wrote:
> On Mon, 4 Sep 2023, Krishna Chaitanya Chundru wrote:
>
>> On 8/17/2023 5:46 PM, Ilpo Järvinen wrote:
>>> Hi all,
>>>
>>> This series adds PCIe bandwidth controller (bwctrl) and associated PCIe
>>> cooling driver to the thermal core side for limiting PCIe link speed
>>> due to thermal reasons. PCIe bandwidth controller is a PCI express bus
>>> port service driver. A cooling device is created for each port the
>>> service driver finds if they support changing speeds.
>> I see we had support for only link speed changes here but we need to add
>> support for
>>
>> link width change also as bandwidth notification from PCIe supports both link
>> speed and link width.
> Hi,
>
> Thanks for the comment. In case you mean that the changes in Link Width
> should be reported correctly, they already are since the sysfs interface
> reads them directly from LNKSTA register.
>
> Or did you perhaps mean that Bandwidth Controller should support also
> changing Link Width? If this is the case I don't know how it can be
> realized so a pointer on how it can be achieved would be appreciated.

Hi,

I didn't have any idea on how thermal framework works.

But as we are adding bandwidth controller support we need to add support 
for width change also, may be we are not using this now, but we may need 
it in the future.

We had similar use case based on the bandwidth requirement on devices 
like WLAN, the client try to reduce or increase the link speed and link 
width.

So in the bandwidth controller driver we can add support for link width 
also. So any client can easily use the driver to change link speed or 
width or both to reduce the power consumption.

Adding link width support should be similar to how you added the link 
speed supported.

Please correct me if I misunderstood something here.

Thanks & Regards,

Krishna Chaitanya.