netdev - Re: [PATCH net 1/4] pegasus: Use heap buffers for all register access

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Date:   Mon, 6 Feb 2017 09:28:22 +0100
From:   Greg KH <greg@...ah.com>
To:     Petko Manolov <petkan@...leusys.com>
Cc:     Ben Hutchings <ben@...adent.org.uk>, netdev@...r.kernel.org,
        linux-usb@...r.kernel.org,
        Lisandro Damián Nicanor Pérez Meyer 
        <lisandro@...ian.org>
Subject: Re: [PATCH net 1/4] pegasus: Use heap buffers for all register access

On Mon, Feb 06, 2017 at 10:14:44AM +0200, Petko Manolov wrote:
> On 17-02-05 01:30:39, Greg KH wrote:
> > On Sat, Feb 04, 2017 at 04:56:03PM +0000, Ben Hutchings wrote:
> > > Allocating USB buffers on the stack is not portable, and no longer
> > > works on x86_64 (with VMAP_STACK enabled as per default).
> > 
> > It's never worked on other platforms, so these should go to the stable 
> > releases please.
> 
> As far as i know both drivers works fine on other platforms, though I only 
> tested it on arm and mipsel. ;)

It all depends on the arm and mips platforms, the ones that can not DMA
from stack memory are the ones that would always fail here (since the
2.2 kernel days).

> Random thought: isn't it better to add the alloc/free code in usb_control_msg() 
> and avoid code duplication all over the driver space?

A very long time ago we considered it, but realized that the majority of
drivers already had the memory dynamically allocated, so we just went
with this.  Perhaps we could revisit that if it turns out we were wrong,
and would simplify things.

thanks,

greg k-h