netdev - Re: [PATCH net-next 2/4] net: ipa: introduce dma_addr

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Date:   Wed, 17 Mar 2021 15:47:47 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Alex Elder <elder@...aro.org>, davem@...emloft.net, kuba@...nel.org
Cc:     bjorn.andersson@...aro.org, evgreen@...omium.org,
        cpratapa@...eaurora.org, subashab@...eaurora.org, elder@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 2/4] net: ipa: introduce dma_addr_high32()



On 3/17/2021 3:29 PM, Alex Elder wrote:
> Create a new helper function to encapsulate extracting the
> high-order 32 bits of a DMA address.  It returns 0 for builds
> in which a DMA address is not 64 bits.
> 
> This avoids doing a 32-position shift on a DMA address if it
> happens not to be 64 bits wide.
> 
> Signed-off-by: Alex Elder <elder@...aro.org>
> ---
>  drivers/net/ipa/gsi.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ipa/gsi.c b/drivers/net/ipa/gsi.c
> index 2119367b93ea9..53698c64cf882 100644
> --- a/drivers/net/ipa/gsi.c
> +++ b/drivers/net/ipa/gsi.c
> @@ -688,6 +688,16 @@ static void gsi_evt_ring_doorbell(struct gsi *gsi, u32 evt_ring_id, u32 index)
>  	iowrite32(val, gsi->virt + GSI_EV_CH_E_DOORBELL_0_OFFSET(evt_ring_id));
>  }
>  
> +/* Encapsulate extracting high-order 32 bits of DMA address */
> +static u32 dma_addr_high32(dma_addr_t addr)
> +{
> +#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
> +	return (u32)(addr >> 32);

You can probably use upper_32bits() here...

> +#else /* !CONFIG_ARCH_DMA_ADDR_T_64BIT */
> +	return 0;
> +#endif /* !CONFIG_ARCH_DMA_ADDR_T_64BIT */
> +}
> +
>  /* Program an event ring for use */
>  static void gsi_evt_ring_program(struct gsi *gsi, u32 evt_ring_id)
>  {
> @@ -711,7 +721,7 @@ static void gsi_evt_ring_program(struct gsi *gsi, u32 evt_ring_id)
>  	val = evt_ring->ring.addr & GENMASK(31, 0);

...and you can use lower_32bits() here.

>  	iowrite32(val, gsi->virt + GSI_EV_CH_E_CNTXT_2_OFFSET(evt_ring_id));
>  
> -	val = evt_ring->ring.addr >> 32;
> +	val = dma_addr_high32(evt_ring->ring.addr);

Does the compiler do a good job at eliminating the assignment when
CONFIG_ARCH_DMA_ADDR_T_64BIT is not defined?

>  	iowrite32(val, gsi->virt + GSI_EV_CH_E_CNTXT_3_OFFSET(evt_ring_id));
>  
>  	/* Enable interrupt moderation by setting the moderation delay */
> @@ -819,7 +829,7 @@ static void gsi_channel_program(struct gsi_channel *channel, bool doorbell)
>  	val = channel->tre_ring.addr & GENMASK(31, 0);
>  	iowrite32(val, gsi->virt + GSI_CH_C_CNTXT_2_OFFSET(channel_id));
>  
> -	val = channel->tre_ring.addr >> 32;
> +	val = dma_addr_high32(channel->tre_ring.addr);
>  	iowrite32(val, gsi->virt + GSI_CH_C_CNTXT_3_OFFSET(channel_id));
>  
>  	/* Command channel gets low weighted round-robin priority */
> 

-- 
Florian