linux-kernel - Re: [PATCH 2/3] usb: host: pci: introduce PCI vendor ID for Netlogic

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Date:   Thu, 15 Mar 2018 10:47:16 +0100
From:   Richard Leitner <richard.leitner@...data.com>
To:     Oliver Neukum <oneukum@...e.com>, Richard Leitner <dev@...l1n.net>,
        <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <linux-usb@...r.kernel.org>
CC:     <bhelgaas@...gle.com>, <mathias.nyman@...el.com>,
        <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 2/3] usb: host: pci: introduce PCI vendor ID for Netlogic


On 03/15/2018 10:26 AM, Oliver Neukum wrote:
> Am Mittwoch, den 14.03.2018, 16:44 +0100 schrieb Richard Leitner:
>> On 03/14/2018 04:27 PM, Oliver Neukum wrote:
>>> Am Mittwoch, den 14.03.2018, 14:31 +0100 schrieb Richard Leitner:
>>>>
>>> Well, but it does not. Removing a redundant definition is a clear
>>> benefit. But you are not removing a definition. You are introducing
>>> a preprocessor constant. Why?
>>> What is its benefit?
>>
>> AFAIK pci_ids.h collects PCI vendor and device IDs in one single 
>> point. As the PCI vendor ID of Netlogic is used in multiple files
>> IMHO it would be a good idea to add it to pci_ids.h and furthermore
>> remove it from arch/mips/include/asm/netlogic/xlp-hal/iomap.h (where
>> it's currently defined).
>>
>> Or am I getting things wrong?
> 
> I think so, yes. We are giving names to constants as a form
> of comment or to change them at multiple places at once and
> consistently.
> 
> So
> 
> #define XYZ_NETDEV_RESET_RETRIES	2
> 
> makes clearly sense. So does
> 
> #define XYZ_MAGIC_VALUE1	0xab4e
> 
> because it tells you that you have a magic value.
> But you will never redefine a PCI vendor ID. In fact you
> must not. And if you have a comparison like
> 
> dev->vID == 0x1234
> 
> if you change this to
> 
> dev->vID == SOME_VENDOR_ID
> 
> what good does this to you? You already knew it was a vendor ID.
> Now you can name it at a glance. So what? If you have a device
> you will have to check whether you have some OEM version. You
> will always go and check the raw number. And if you have a log
> and need to check whether the check will be true, you will have
> a number.
> Using a constant there is nothing but trouble. Yet one more grep.

Thank you for that explanation. But IMHO it was clearer with a
human-readable name in such comparisons...

For example in the following I see at the first glance which
device from which vendor is affected and I don't need any
additional comments or ID databases...
       if (pdev->vendor == PCI_VENDOR_ID_TI &&
           pdev->device == PCI_DEVICE_ID_TI_TUSB73X0)

...but if that's not the preferred way of doing things I'm
perfectly fine with that.

Furthermore to me it sounds you are saying that the complete
pci_ids.h should be thrown over-board?!?

regards;richard.l