linux-kernel - Re: Subject: [PATCH] pci/msi: remove redundant calculation in msi_setup_msi

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Date:   Wed, 23 Aug 2023 16:15:27 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     黄少波 <huangshaobo3@...omi.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Ahmed S. Darwish" <darwi@...utronix.de>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Kevin Tian <kevin.tian@...el.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     李高鹏 <chenwei29@...omi.com>,
        梁伟鹏 <weipengliang@...omi.com>,
        翁金飞 <wengjinfei@...omi.com>,
        熊亮 <xiongliang@...omi.com>
Subject: Re: Subject: [PATCH] pci/msi: remove redundant calculation in
 msi_setup_msi_desc

On Fri, Aug 18 2023 at 07:26, 黄少波 wrote:

Your patch is corrupt:

 Applying: Subject: [PATCH] pci/msi: remove redundant calculation in msi_setup_msi_desc
 error: corrupt patch at line 12

It's DOS mangled and whitespace damaged.

> Whether to support 64-bit address status has been calculated before,
> and the calculation result can be used directly afterwards, so use
> msi_attrib.is_64 to avoid double calculation.

I'm not seeing what this solves:

> -       if (control & PCI_MSI_FLAGS_64BIT)
> +       if (desc.pci.msi_attrib.is_64)

Both variants resolve to a test of a bit and a conditional instruction
on the result. It's exactly zero difference in terms of "calculation".

So all this does is change the memory location to test. Not more not
less. It does not generate better code and does not save anything.

Thanks,

        tglx