linux-kernel - Re: [PATCH v9 1/3] dmaengine: ptdma: Initial driver for the AMD PTDMA

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 16 Jun 2021 09:17:06 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Sanjay R Mehta <sanmehta@....com>
Cc:     Vinod Koul <vkoul@...nel.org>,
        Sanjay R Mehta <Sanju.Mehta@....com>,
        dan.j.williams@...el.com, Thomas.Lendacky@....com,
        Shyam-sundar.S-k@....com, Nehal-bakulchandra.Shah@....com,
        robh@...nel.org, mchehab+samsung@...nel.org, davem@...emloft.net,
        linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org
Subject: Re: [PATCH v9 1/3] dmaengine: ptdma: Initial driver for the AMD PTDMA

On Wed, Jun 16, 2021 at 12:27:32PM +0530, Sanjay R Mehta wrote:
> 
> 
> On 6/16/2021 11:46 AM, Greg KH wrote:
> > [CAUTION: External Email]
> > 
> > On Wed, Jun 16, 2021 at 10:24:52AM +0530, Sanjay R Mehta wrote:
> >>
> >>
> >> On 6/16/2021 9:45 AM, Vinod Koul wrote:
> >>> [CAUTION: External Email]
> >>>
> >>> On 15-06-21, 16:50, Sanjay R Mehta wrote:
> >>>
> >>>>>> +static struct pt_device *pt_alloc_struct(struct device *dev)
> >>>>>> +{
> >>>>>> +     struct pt_device *pt;
> >>>>>> +
> >>>>>> +     pt = devm_kzalloc(dev, sizeof(*pt), GFP_KERNEL);
> >>>>>> +
> >>>>>> +     if (!pt)
> >>>>>> +             return NULL;
> >>>>>> +     pt->dev = dev;
> >>>>>> +     pt->ord = atomic_inc_return(&pt_ordinal);
> >>>>>
> >>>>> What is the use of this number?
> >>>>>
> >>>>
> >>>> There are eight similar instances of this DMA engine on AMD SOC.
> >>>> It is to differentiate each of these instances.
> >>>
> >>> Are they individual device objects?
> >>>
> >>
> >> Yes, they are individual device objects.
> > 
> > Then what is "ord" for?  Why are you using an atomic variable for this?
> > What does this field do?  Why doesn't the normal way of naming a device
> > come into play here instead?
> > 
> 
> Hi Greg,
> 
> The value of "ord" is incremented for each device instance and then it
> is used to store different name for each device as shown in below snippet.
> 
> 	pt->ord = atomic_inc_return(&pt_ordinal);
> 	snprintf(pt->name, MAX_PT_NAME_LEN, "pt-%u", pt->ord);

Why not use an idr structure like this like all other drivers do?  That
way when devices are removed the numbers are properly reused as well.

And why do you need to save the value?

thanks,

greg k-h