linux-kernel - RE: [PATCH] dmaengine: dw-edma: fix unnecessary stack usage

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Date:   Fri, 21 Jun 2019 08:21:33 +0000
From:   Gustavo Pimentel <Gustavo.Pimentel@...opsys.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Gustavo Pimentel <Gustavo.Pimentel@...opsys.com>,
        Vinod Koul <vkoul@...nel.org>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] dmaengine: dw-edma: fix unnecessary stack usage

Hi,

On Mon, Jun 17, 2019 at 14:16:45, Arnd Bergmann <arnd@...db.de> wrote:

> Putting large constant data on the stack causes unnecessary overhead
> and stack usage:
> 
> drivers/dma/dw-edma/dw-edma-v0-debugfs.c:285:6: error: stack frame size of 1376 bytes in function 'dw_edma_v0_debugfs_on' [-Werror,-Wframe-larger-than=]

I had that warning at the beginning of the development, that's why I 
divided the debugfs entries into several subfunctions. Perhaps my 
configuration has configured a bigger stack frame size than your 
configuration.

> 
> Mark the variable 'static const' in order for the compiler to move it
> into the .rodata section where it does no such harm.

Ok, sounds good.
Thanks.

> 
> Fixes: 305aebeff879 ("dmaengine: Add Synopsys eDMA IP version 0 debugfs support")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/dma/dw-edma/dw-edma-v0-debugfs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/dw-edma/dw-edma-v0-debugfs.c b/drivers/dma/dw-edma/dw-edma-v0-debugfs.c
> index affa1ccaf7a0..42739508c0d8 100644
> --- a/drivers/dma/dw-edma/dw-edma-v0-debugfs.c
> +++ b/drivers/dma/dw-edma/dw-edma-v0-debugfs.c
> @@ -48,7 +48,7 @@ static struct {
>  } lim[2][EDMA_V0_MAX_NR_CH];
>  
>  struct debugfs_entries {
> -	char					name[24];
> +	const char				*name;
>  	dma_addr_t				*reg;
>  };
>  
> -- 
> 2.20.0