linux-kernel - Re: [PATCH v2 09/10] PCI: keystone: Exit ks_pcie_probe() for the default switch-case of "mode"

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Message-ID: <9d931573-5b23-44cf-8798-58715f9be699@ti.com>
Date: Sat, 20 Sep 2025 14:08:58 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: Manivannan Sadhasivam <mani@...nel.org>
CC: Siddharth Vadapalli <s-vadapalli@...com>, <lpieralisi@...nel.org>,
        <kwilczynski@...nel.org>, <robh@...nel.org>, <bhelgaas@...gle.com>,
        <jingoohan1@...il.com>, <christian.bruel@...s.st.com>,
        <qiang.yu@....qualcomm.com>, <mayank.rana@....qualcomm.com>,
        <thippeswamy.havalige@....com>, <shradha.t@...sung.com>,
        <quic_schintav@...cinc.com>, <inochiama@...il.com>,
        <cassel@...nel.org>, <kishon@...nel.org>,
        <sergio.paracuellos@...il.com>, <18255117159@....com>,
        <rongqianfeng@...o.com>, <jirislaby@...nel.org>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <srk@...com>
Subject: Re: [PATCH v2 09/10] PCI: keystone: Exit ks_pcie_probe() for the
 default switch-case of "mode"

On Sat, Sep 20, 2025 at 01:57:34PM +0530, Manivannan Sadhasivam wrote:
> On Sat, Sep 20, 2025 at 01:39:22PM +0530, Siddharth Vadapalli wrote:
> > On Sat, Sep 20, 2025 at 12:06:46AM +0530, Manivannan Sadhasivam wrote:
> > > On Fri, Sep 12, 2025 at 05:46:20PM +0530, Siddharth Vadapalli wrote:
> > > > In ks_pcie_probe(), the switch-case for the "mode" is used to configure
> > > > the PCIe Controller for either Root-Complex or Endpoint mode of operation.
> > > > Prior to the switch-case statement for "mode" an invalid mode will result
> > > > in probe failure only if "dw_pcie_ver_is_ge(pci, 480A)" is true, which
> > > > is the case for the AM654 platform. On the other hand, when that is not
> > > > the case, "ks_pcie_set_mode()" will be invoked, which does not validate
> > > > the mode. As a result, it is possible for the switch-case statement for
> > > > "mode" to receive an invalid mode. Currently, an error message is displayed
> > > > in the "default" case where "mode" is neither "DW_PCIE_RC_TYPE" nor
> > > > "DW_PCIE_EP_TYPE", but the probe succeeds. However, since the configuration
> > > > required for Root-Complex and Endpoint mode have not been performed, the
> > > > Controller is not operational.
> > > > 
> > > > Fix this by exiting "ks_pcie_probe()" with the return value of "-EINVAL"
> > > > in addition to displaying the existing error message.
> > > > 
> > > > Signed-off-by: Siddharth Vadapalli <s-vadapalli@...com>
> > > 
> > > Fixes tag? And probably CC stable since the controller seems to be not
> > > operations without this fix.
> > 
> > While I had mentioned the rationale for not including the 'Fixes tag' in
> > the v1 patch below the tearline, I forgot to add it in this patch. I will
> > quote the same below:
> > 
> >     NOTE: A "Fixes" tag is ommitted on purpose since the fix is not crucial:
> >     1. It doesn't fix a crash or any fatal error
> >     2. It doesn't enable controller functionality by fixing the issue
> > 
> 
> Fixes tag should be added irrespective of the cruciality of the bug.

Ok, I will include the tag in the v3 series.

> 
> >     Therefore, the patch may not be worth backporting.
> > 
> 
> Agree with this though.
> 
> > Prior to this patch, the probe succeeded and the controller was
> > unusable. Post this patch, the probe will fail and the controller is
> > still unusable. Behavior is identical from a usability perspective but
> > the user is aware of the issue since the probe fails.
> > 
> 
> Ok. I think the description could reworded to make it more clear. The actual
> issue is that the default case lacks setting the errno, leading to probe
> success. But the addition of ks_pcie_set_mode() and others seem to cause little
> bit confusion.

I will update the commit message and keep it concise to highlight the
issue. I understand that the additional information provided in order to
set the context might have been counterproductive.

Thank you for reviewing the patch and providing feedback.

Regards,
Siddharth.