linux-kernel - Re: [PATCH v7 1/8] PCI: Add pcie_reset_flr to follow calling convention of other reset methods

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Message-ID: <20210624122309.GA3518896@bjorn-Precision-5520>
Date:   Thu, 24 Jun 2021 07:23:09 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Amey Narkhede <ameynarkhede03@...il.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, alex.williamson@...hat.com,
        Raphael Norwitz <raphael.norwitz@...anix.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        kw@...ux.com, Shanker Donthineni <sdonthineni@...dia.com>,
        Sinan Kaya <okaya@...nel.org>, Len Brown <lenb@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v7 1/8] PCI: Add pcie_reset_flr to follow calling
 convention of other reset methods

On Tue, Jun 08, 2021 at 11:18:50AM +0530, Amey Narkhede wrote:
> Currently there is separate function pcie_has_flr() to probe if pcie flr is
> supported by the device which does not match the calling convention
> followed by reset methods which use second function argument to decide
> whether to probe or not.  Add new function pcie_reset_flr() that follows
> the calling convention of reset methods.

> +/**
> + * pcie_reset_flr - initiate a PCIe function level reset
> + * @dev: device to reset
> + * @probe: If set, only check if the device can be reset this way.
> + *
> + * Initiate a function level reset on @dev.
> + */
> +int pcie_reset_flr(struct pci_dev *dev, int probe)
> +{
> +	u32 cap;
> +
> +	if (dev->dev_flags & PCI_DEV_FLAGS_NO_FLR_RESET)
> +		return -ENOTTY;
> +
> +	pcie_capability_read_dword(dev, PCI_EXP_DEVCAP, &cap);
> +	if (!(cap & PCI_EXP_DEVCAP_FLR))
> +		return -ENOTTY;
> +
> +	if (probe)
> +		return 0;
> +
> +	return pcie_flr(dev);
> +}

Tangent: I've been told before, but I can't remember why we need the
"probe" interface.  Since we're looking at this area again, can we add
a comment to clarify this?

Every time I read this, I wonder why we can't just get rid of the
probe and attempt a reset.  If it fails because it's not supported, we
could just try the next one in the list.