linux-kernel - Re: [PATCH v1] PCI: Add PCIE_CONFIG_REQUEST_WAIT

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Date:   Wed, 29 Nov 2023 17:21:08 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Kevin Xie <kevin.xie@...rfivetech.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, mason.huo@...rfivetech.com,
        leyfoon.tan@...rfivetech.com, minda.chen@...rfivetech.com
Subject: Re: [PATCH v1] PCI: Add PCIE_CONFIG_REQUEST_WAIT_MS waiting time
 value

On Fri, Nov 24, 2023 at 09:45:08AM +0800, Kevin Xie wrote:
> Add the PCIE_CONFIG_REQUEST_WAIT_MS marco to define the minimum waiting
> time between sending the first configuration request to the device and
> exit from a conventional reset (or after link training completes).

s/marco/macro/

List the first event before the second one, i.e., the delay is from
exit from reset to the config request.

> As described in the conventional reset rules of PCI specifications,
> there are two different use cases of the value:
> 
>    - With a downstream port that supports link speeds <= 5.0 GT/s,
>      the waiting is following exit from a conventional reset.
> 
>    - With a downstream port that supports link speeds > 5.0 GT/s,
>      the waiting is after link training completes.

Include the spec citation here as well as in the comment below.

I assume there are follow-on patches that actually use this?  Can we
make this the first patch in a series so we know we don't have an
unused macro lying around?

> Signed-off-by: Kevin Xie <kevin.xie@...rfivetech.com>
> Reviewed-by: Mason Huo <mason.huo@...rfivetech.com>
> ---
>  drivers/pci/pci.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 5ecbcf041179..4ca8766e546e 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -22,6 +22,13 @@
>   */
>  #define PCIE_PME_TO_L2_TIMEOUT_US	10000
>  
> +/*
> + * PCIe r6.0, sec 6.6.1, <Conventional Reset>
> + * Requires a minimum waiting of 100ms before sending a configuration
> + * request to the device.
> + */
> +#define PCIE_CONFIG_REQUEST_WAIT_MS	100
> +
>  extern const unsigned char pcie_link_speed[];
>  extern bool pci_early_dump;
>  
> -- 
> 2.25.1
>