Subject: Re: [PATCH v2 2/2] spi: aspeed: Replace VLA parameter with flat pointer in calibration helper

From: David Laight <[email-masked]>
Date: Fri, 22 May 2026 09:19:15 +0100

On Fri, 22 May 2026 15:16:21 +0800
Chin-Ting Kuo <[email-masked]> wrote:

> aspeed_spi_ast2600_optimized_timing() declared its buffer argument as a
> variable-length array parameter (u8 buf[rows][cols]), which causes a
> sparse warning. Replace the VLA parameter with a plain u8 * and compute
> the 2-D index manually. The corresponding call site is also updated.

This code is all a bit horrid.
The 6 and 17 (which are also used in the array declaration) have to match the
TIMING_DELAY_HCYCLE_MAX and TIMING_DELAY_INPUT_MAX values used for the loops.

In any case the code would be more obvious if the 'run length' of test
passes was counted during the initial loop.
Looks like it wants at least 4 ones, after you've got that many
(and a fail) there is little point continuing the delay loop for
that hcycle.

-- David

> 
> Reported-by: kernel test robot <[email-masked]>
> Closes: https://lore.kernel.org/oe-kbuild-all/[email-masked]/
> Signed-off-by: Chin-Ting Kuo <[email-masked]>
> Reviewed-by: Cédric Le Goater <[email-masked]>
> ---
>  drivers/spi/spi-aspeed-smc.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/spi/spi-aspeed-smc.c b/drivers/spi/spi-aspeed-smc.c
> index 808659a1f460..027caa2eeb5c 100644
> --- a/drivers/spi/spi-aspeed-smc.c
> +++ b/drivers/spi/spi-aspeed-smc.c
> @@ -1467,8 +1467,7 @@ static int aspeed_spi_do_calibration(struct aspeed_spi_chip *chip)
>   * must contains the highest number of consecutive "pass"
>   * results and not span across multiple rows.
>   */
> -static u32 aspeed_spi_ast2600_optimized_timing(u32 rows, u32 cols,
> -					       u8 buf[rows][cols])
> +static u32 aspeed_spi_ast2600_optimized_timing(u32 rows, u32 cols, u8 *buf)
>  {
>  	int r = 0, c = 0;
>  	int max = 0;
> @@ -1478,7 +1477,7 @@ static u32 aspeed_spi_ast2600_optimized_timing(u32 rows, u32 cols,
>  		for (j = 0; j < cols;) {
>  			int k = j;
>  
> -			while (k < cols && buf[i][k])
> +			while (k < cols && buf[(i * cols) + k])
>  				k++;
>  
>  			if (k - j > max) {
> @@ -1541,7 +1540,7 @@ static int aspeed_spi_ast2600_calibrate(struct aspeed_spi_chip *chip, u32 hdiv,
>  		}
>  	}
>  
> -	calib_point = aspeed_spi_ast2600_optimized_timing(6, 17, calib_res);
> +	calib_point = aspeed_spi_ast2600_optimized_timing(6, 17, &calib_res[0][0]);
>  	/* No good setting for this frequency */
>  	if (calib_point == 0)
>  		return -1;