linux-kernel - Re: [PATCH 3/4] AHCI: Conserve interrupts with pci_enable_msi_block

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Date:	Tue, 3 Sep 2013 10:18:24 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Alexander Gordeev <agordeev@...hat.com>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	linux-pci@...r.kernel.org, linux-ide@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>, Joerg Roedel <joro@...tes.org>,
	Jan Beulich <JBeulich@...e.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 3/4] AHCI: Conserve interrupts with
 pci_enable_msi_block_part() interface

On Mon, Sep 02, 2013 at 11:00:28AM +0200, Alexander Gordeev wrote:
> +	if (hpriv->flags & AHCI_HFLAG_NO_MSI)
> +		goto intx;
> +
> +	rc = pci_enable_msi_block_part(pdev, n_ports, AHCI_MAX_PORTS);
> +	if (!rc)
> +		return AHCI_MAX_PORTS;
> +	if (rc < 0)
> +		goto intx;
> +
> +	maxvec = rc;
> +	rc = pci_enable_msi_block_part(pdev, n_ports, maxvec);
> +	if (!rc)
> +		return maxvec;
> +	if (rc < 0)
> +		goto intx;

Why is the above fallback necessary?  The only other number which
makes sense is roundup_pow_of_two(n_ports), right?  What does the
above fallback logic buy us?

Thanks.

-- 
tejun
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