Re: [PATCH V1] PCI: dwc: Use dev_info for PCIe link down event logging

From: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
To: Jon Hunter <jonathanh@nvidia.com>
Cc: Vidya Sagar <vidyas@nvidia.com>,
	Bjorn Helgaas <helgaas@kernel.org>,
	jingoohan1@gmail.com, gustavo.pimentel@synopsys.com,
	lpieralisi@kernel.org, robh@kernel.org, kw@linux.com,
	bhelgaas@google.com, treding@nvidia.com,
	linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
	kthota@nvidia.com, mmaddireddy@nvidia.com, sagar.tv@gmail.com
Subject: Re: [PATCH V1] PCI: dwc: Use dev_info for PCIe link down event logging
Date: Wed, 14 Sep 2022 17:13:06 +0530	[thread overview]
Message-ID: <20220914114306.GG16459@workstation> (raw)
In-Reply-To: <5ffe3dfa-28a5-a5fc-0ae2-28927c39dc03@nvidia.com>

On Wed, Sep 14, 2022 at 12:25:51PM +0100, Jon Hunter wrote:
> 
> On 14/09/2022 12:18, Manivannan Sadhasivam wrote:
> > On Wed, Sep 14, 2022 at 04:32:10PM +0530, Vidya Sagar wrote:
> > > Agree with Mani.
> > > Not all form factors support PRSNT pin (Ex:- M.2 Key-M form factor) and even
> > > if the slot form factor supports PRSNT, it is not mandatory to have a GPIO
> > > routed to the PRSNT pin of the slot.
> > 
> > Right.
> > 
> > > Also, since these are development platforms, we wouldn't want to keep
> > > changing a controller's status in the DT, instead want to know the device's
> > > presence/absence (by way of link up) looking at the log.
> > > In my honest opinion, I don't think the absence of a device in the slot
> > > should be treated as an error.
> > > 
> > 
> > As I mentioned earlier, timeout can happen due to an issue with PHY layer
> > also. In those cases, "dev_err()" is relevant.
> > 
> > And I also agree that absence of the device should not be treated as an
> > error. But my question is, if you know that the slot is going to be
> > empty always, why cannot you just disable it in dts?
> 
> I really don't think that makes sense from a usability perspective. You want
> to allow users to connect PCI cards and for them to work without having to
> update the DTB. I have plenty of open PCI slots on my PC and I would be a
> bit upset if someone told me I need to update the PC firmware each time I
> wanted to use a new slot.
> 

My question was, "do you think the slot is going to be empty always".
This can happen with slots exposed through a connector (not a PCIe one) and
users would plug in add-on cards for accessing the slots. In those
cases, the add-on specific devicetree can enable the PCIe instance and
use it.

But from your reply, I can infer that the slot is exposed on a standard
PCIe connector and users would connect a PCIe device any time.

Anyway, I don't strongly object the change and leave it to the
maintainers to decide.

Thanks,
Mani

> Jon
> 
> -- 
> nvpublic