On Thu, Nov 03, 2022 at 10:55:27AM +0300, Dan Carpenter wrote:
> On Thu, Nov 03, 2022 at 12:57:09PM +0530, Deepak R Varma wrote:
> > Hello,
> > While reviewing this [1] coccicheck warning, I observed something that concerned
> > me. The variable i_write_length is declared to be of u32 type. Later it is
> > assigned a value DMA_MAX_COUNT * mpkt; which is 256 * u32;
> >
> > I am unable to estimate if mpkt (or max packet size) can attain value greater
> > than 16777215 in which case the result will overflow the 32 bits of
> > i_write_length. Is it safe to make i_write_length to be a u64?
> >
> > [1] drivers/staging/emxx_udc/emxx_udc.c:1007:28-29: WARNING opportunity for min()
> >
>
> drivers/staging/emxx_udc/emxx_udc.c
> 983 static int _nbu2ss_in_dma(struct nbu2ss_udc *udc, struct nbu2ss_ep *ep,
> 984 struct nbu2ss_req *req, u32 num, u32 length)
> 985 {
> 986 dma_addr_t p_buffer;
> 987 u32 mpkt; /* MaxPacketSize */
> 988 u32 lmpkt; /* Last Packet Data Size */
> 989 u32 dmacnt; /* IN Data Size */
> 990 u32 i_write_length;
> 991 u32 data;
> 992 int result = -EINVAL;
> 993 struct fc_regs __iomem *preg = udc->p_regs;
> 994
> 995 if (req->dma_flag)
> 996 return 1; /* DMA is forwarded */
> 997
> 998 #ifdef USE_DMA
> 999 if (req->req.actual == 0)
> 1000 _nbu2ss_dma_map_single(udc, ep, req, USB_DIR_IN);
> 1001 #endif
> 1002 req->dma_flag = true;
> 1003
> 1004 /* MAX Packet Size */
> 1005 mpkt = _nbu2ss_readl(&preg->EP_REGS[num].EP_PCKT_ADRS) & EPN_MPKT;
> ^^^^^^^^
> mpkt is 0-0x7ff so 256 * 0x7ff will not be greater than UINT_MAX.
Thank you Dan. I understand now. "& EPN_MPKT" keeps the size under control.
Appreciate very much.
./drv
>
> 1006
> 1007 if ((DMA_MAX_COUNT * mpkt) < length)
> 1008 i_write_length = DMA_MAX_COUNT * mpkt;
> 1009 else
> 1010 i_write_length = length;
> 1011
> 1012 /*------------------------------------------------------------*/
> 1013 /* Number of transmission packets */
> 1014 if (mpkt < i_write_length) {
>
> regards,
> dan carpenter
>
