linux-kernel - Re: [PATCH 1/1] PCI: Fix Extend ACS configurability

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Message-ID: <20250113200749.GW5556@nvidia.com>
Date: Mon, 13 Jan 2025 16:07:49 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Tushar Dave <tdave@...dia.com>
Cc: corbet@....net, bhelgaas@...gle.com, paulmck@...nel.org,
	akpm@...ux-foundation.org, thuth@...hat.com, rostedt@...dmis.org,
	xiongwei.song@...driver.com, vidyas@...dia.com,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, vsethi@...dia.com,
	sdonthineni@...dia.com
Subject: Re: [PATCH 1/1] PCI: Fix Extend ACS configurability

On Wed, Jan 08, 2025 at 07:13:34PM -0800, Tushar Dave wrote:
> > Yes, but X in config_acs should copy the FW value not the value
> > modified by disable_acs_redir_param
> 
> I see your point. In that case (for the last hunk in my patch) something
> like this should work IMO.
> 
> -       /* If mask is 0 then we copy the bit from the firmware setting. */
> -       caps->ctrl = (caps->ctrl & ~mask) | (caps->fw_ctrl & mask);
> -       caps->ctrl |= flags;
> +       /* For unchanged ACS bits 'x' or 'X', copy the bits from the
> firmware setting. */
> +        if (!acs_mask)
> +                caps->ctrl = caps->fw_ctrl;
> +
> +       caps->ctrl &= ~mask;
> +       caps->ctrl |= (flags & mask);
> 
> Wish I can have better condition check instead of 'if (!acs_mask)' but let
> me know your thoughts.

It should be per-bit surely? I think the original logic was the right
idea, just the bit logic had the wrong operators..

Jason