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Re: [PATCH v2 1/2] hw/dma: sifive_pdma: Fix Control.claim bit detection


From: Philippe Mathieu-Daudé
Subject: Re: [PATCH v2 1/2] hw/dma: sifive_pdma: Fix Control.claim bit detection
Date: Mon, 27 Sep 2021 14:56:23 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.1.0

On 9/27/21 09:21, Bin Meng wrote:
> At present the codes detect whether the DMA channel is claimed by:
> 
>   claimed = !!s->chan[ch].control & CONTROL_CLAIM;
> 
> As ! has higher precedence over & (bitwise and), this is essentially
> 
>   claimed = (!!s->chan[ch].control) & CONTROL_CLAIM;
> 
> which is wrong, as any non-zero bit set in the control register will
> produce a result of a claimed channel.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

Maybe worth adding:

Reported using GCC 9.3.0 on Ubuntu 20.04:

  suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’
to ‘~’ [-Werror=parentheses]

> Fixes: de7c7988d25d ("hw/dma: sifive_pdma: reset Next* registers when 
> Control.claim is set")
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> 
> ---
> 
> Changes in v2:
> - reword the commit message
> 
>  hw/dma/sifive_pdma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
> index b4fd40573a..b8ec7621f3 100644
> --- a/hw/dma/sifive_pdma.c
> +++ b/hw/dma/sifive_pdma.c
> @@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
>      offset &= 0xfff;
>      switch (offset) {
>      case DMA_CONTROL:
> -        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
> +        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
>  
>          if (!claimed && (value & CONTROL_CLAIM)) {
>              /* reset Next* registers */
> 



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