linux-kernel - Re: [PATCH v3] staging: gdm724x: Fix DMA from stack

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Date:   Wed, 10 Feb 2021 20:31:33 +0530
From:   Amey Narkhede <ameynarkhede03@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        dan.carpenter@...cle.com
Subject: Re: [PATCH v3] staging: gdm724x: Fix DMA from stack

On 21/02/10 03:55PM, Greg KH wrote:
> On Wed, Feb 10, 2021 at 07:55:12PM +0530, Amey Narkhede wrote:
> > Stack allocated buffers cannot be used for DMA
> > on all architectures so allocate hci_packet buffer
> > using kmalloc.
> >
> > Signed-off-by: Amey Narkhede <ameynarkhede03@...il.com>
> > ---
> > Changes in v3:
> > 	- Remove superfluous buf pointer
> > 	- Reduce size of allocation of hci_packet to match number of
> > 	bytes used for DMA
> >
> >  drivers/staging/gdm724x/gdm_usb.c | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/staging/gdm724x/gdm_usb.c b/drivers/staging/gdm724x/gdm_usb.c
> > index dc4da66c3..80c58a3ef 100644
> > --- a/drivers/staging/gdm724x/gdm_usb.c
> > +++ b/drivers/staging/gdm724x/gdm_usb.c
> > @@ -56,20 +56,24 @@ static int gdm_usb_recv(void *priv_dev,
> >
> >  static int request_mac_address(struct lte_udev *udev)
> >  {
> > -	u8 buf[16] = {0,};
> > -	struct hci_packet *hci = (struct hci_packet *)buf;
> > +	struct hci_packet *hci;
> >  	struct usb_device *usbdev = udev->usbdev;
> >  	int actual;
> >  	int ret = -1;
> >
> > +	hci = kmalloc(5, GFP_KERNEL);
>
> Why "5" and not:
> 	hci = kmalloc(sizeof(*hci), GFP_KERNEL);
> ?
>
> thanks,
>
> greg k-h
I really need a cup of coffee :)
I'll send v4

Thanks,
Amey

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