Re: [PATCH 1/2] net/txgbe: add vectorized functions for Rx/Tx

[Tyler Retzlaff <roretzla@linux.microsoft.com>]

On Thu, Mar 21, 2024 at 04:27:26PM +0000, Ferruh Yigit wrote:
> On 3/5/2024 8:10 AM, Jiawen Wu wrote:
> 
> <...>
> 
> >>> +++ b/drivers/net/txgbe/txgbe_rxtx_vec_neon.c
> >>> @@ -0,0 +1,604 @@
> >>> +/* SPDX-License-Identifier: BSD-3-Clause
> >>> + * Copyright(c) 2015-2024 Beijing WangXun Technology Co., Ltd.
> >>> + * Copyright(c) 2010-2015 Intel Corporation
> >>> + */
> >>> +
> >>> +#include <ethdev_driver.h>
> >>> +#include <rte_malloc.h>
> >>> +#include <rte_vect.h>
> >>> +
> >>> +#include "txgbe_ethdev.h"
> >>> +#include "txgbe_rxtx.h"
> >>> +#include "txgbe_rxtx_vec_common.h"
> >>> +
> >>> +#pragma GCC diagnostic ignored "-Wcast-qual"
> >>> +
> >>
> >> Is this pragma really required?
> > 
> > Yes. Otherwise, there are warnings in the compilation:
> > 
> > [1909/2921] Compiling C object drivers/libtmp_rte_net_txgbe.a.p/net_txgbe_txgbe_rxtx_vec_neon.c.o
> > ../drivers/net/txgbe/txgbe_rxtx_vec_neon.c: In function ‘txgbe_rxq_rearm’:
> > ../drivers/net/txgbe/txgbe_rxtx_vec_neon.c:37:15: warning: cast discards ‘volatile’ qualifier from pointer target type [-Wcast-qual]
> >      vst1q_u64((uint64_t *)&rxdp[i], zero);
> >                ^
> > ../drivers/net/txgbe/txgbe_rxtx_vec_neon.c:60:13: warning: cast discards ‘volatile’ qualifier from pointer target type [-Wcast-qual]
> >    vst1q_u64((uint64_t *)rxdp++, dma_addr0);
> >              ^
> > ../drivers/net/txgbe/txgbe_rxtx_vec_neon.c:65:13: warning: cast discards ‘volatile’ qualifier from pointer target type [-Wcast-qual]
> >    vst1q_u64((uint64_t *)rxdp++, dma_addr1);
> > 
> 
> Hi Honnappa,
> 
> There are multiple drivers ignores "-Wcast-qual" for neon implementation.
> 
> Is there a better, more proper way to address this warning?

rather than suppress the warning you could just cast away the volatile
qualifier the common approach is to cast through uintptr_t to discard.

volatile uint64_t *vp;
uint64_t *p = (uint64_t *)(uintptr_t)vp;

perhaps better than broad suppression of warnings. but does require code
be reviewed to be certain it is okay to have the qualifier removed which
i suspect is okay in functions that are inline assembly or intrinsics.

> 
> 
> Thanks,
> ferruh