Re: [PATCH] PCI: j721e: Fix the value of linkdown_irq_regfield for J784S4

[Bjorn Helgaas <helgaas@kernel.org>]

[+to Matt, author of e49ad667815d]

On Wed, Mar 05, 2025 at 06:50:18PM +0530, Siddharth Vadapalli wrote:
> Commit under Fixes assigned the value of 'linkdown_irq_regfield' for the
> J784S4 SoC as 'LINK_DOWN' which corresponds to BIT(1). However, according
> to the Technical Reference Manual and Register Documentation for the J784S4
> SoC [0], BIT(1) corresponds to "ENABLE_SYS_EN_PCIE_DPA_1" which is __NOT__
> the field for the link-state interrupt. Instead, it is BIT(10) of the
> "PCIE_INTD_ENABLE_REG_SYS_2" register that corresponds to the link-state
> field named as "ENABLE_SYS_EN_PCIE_LINK_STATE".

I guess the reason we want this is that on J784S4, we ignore actual
link-down interrupts (and we don't write STATUS_CLR_REG_SYS_2 to clear
the interrupt indication, so maybe there's an interrupt storm), and we
think some other interrupt (DPA_1, whatever that is) is actually a
link-down interrupt?

> Hence, set 'linkdown_irq_regfield' to the macro 'J7200_LINK_DOWN' which
> expands to BIT(10) and was first defined for the J7200 SoC. Other SoCs
> already reuse this macro since it accurately represents the link-state
> field in their respective "PCIE_INTD_ENABLE_REG_SYS_2" register.
> 
> [0]: https://www.ti.com/lit/zip/spruj52

Thanks for the spec URL.  Can you include a relevant section number?
I searched for some of this stuff but couldn't find it.

Since I have low confidence that the URL will be valid after a few
years, I wish the spec also had a human-readable name and revision
number.  But maybe the alphabet soup or "SPRUJ52D", "revised July
2024" is all we can hope for.

> Fixes: e49ad667815d ("PCI: j721e: Add TI J784S4 PCIe configuration")
> Cc: stable@vger.kernel.org
> Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
> ---
> 
> Hello,
> 
> This patch is based on commit
> 48a5eed9ad58 Merge tag 'devicetree-fixes-for-6.14-2' of git://git.kernel.org/pub/scm/linux/kernel/git/robh/linux
> of the master branch of Linux.
> 
> Patch has been tested on J784S4-EVM, validating that disconnecting an
> Endpoint Device connected to J784S4-EVM results in the following message
> on the J784S4-EVM:
> 	j721e-pcie 2900000.pcie: LINK DOWN!
> which wasn't seen earlier.
> 
> Regards,
> Siddharth.
> 
>  drivers/pci/controller/cadence/pci-j721e.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
> index 0341d51d6aed..1da9d9918d0d 100644
> --- a/drivers/pci/controller/cadence/pci-j721e.c
> +++ b/drivers/pci/controller/cadence/pci-j721e.c
> @@ -376,13 +376,13 @@ static const struct j721e_pcie_data j784s4_pcie_rc_data = {
>  	.mode = PCI_MODE_RC,
>  	.quirk_retrain_flag = true,
>  	.byte_access_allowed = false,
> -	.linkdown_irq_regfield = LINK_DOWN,
> +	.linkdown_irq_regfield = J7200_LINK_DOWN,
>  	.max_lanes = 4,
>  };
>  
>  static const struct j721e_pcie_data j784s4_pcie_ep_data = {
>  	.mode = PCI_MODE_EP,
> -	.linkdown_irq_regfield = LINK_DOWN,
> +	.linkdown_irq_regfield = J7200_LINK_DOWN,
>  	.max_lanes = 4,
>  };
>  
> -- 
> 2.34.1
>