[PATCH] firmware: arm_ffa: Use the correct buffer size during RXTX_MAP

[Sudeep Holla]

On Wed, Apr 01, 2026 at 11:17:38AM +0000, Sebastian Ene wrote:
> Don't use the discovered buffer size from an FFA_FEATURES call directly
> since we can run on a system that has the PAGE_SIZE larger than the
> returned size which makes the alloc_pages_exact for the buffer to be
> rounded up.
> 
> Fixes: 61824feae5c0 ("firmware: arm_ffa: Fetch the Rx/Tx buffer size using ffa_features()")
> Signed-off-by: Sebastian Ene <sebastianene at google.com>
> ---
>  drivers/firmware/arm_ffa/driver.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/arm_ffa/driver.c b/drivers/firmware/arm_ffa/driver.c
> index f2f94d4d533e..d0c926aca120 100644
> --- a/drivers/firmware/arm_ffa/driver.c
> +++ b/drivers/firmware/arm_ffa/driver.c
> @@ -2078,7 +2078,7 @@ static int __init ffa_init(void)
>  
>  	ret = ffa_rxtx_map(virt_to_phys(drv_info->tx_buffer),
>  			   virt_to_phys(drv_info->rx_buffer),
> -			   rxtx_bufsz / FFA_PAGE_SIZE);
> +			   DIV_ROUND_UP(rxtx_bufsz, PAGE_SIZE) / FFA_PAGE_SIZE);

Did you mean to use PAGE_ALIGN() instead of DIV_ROUND_UP() ?

The new pg_cnt calculation is dimensionally incorrect and evaluates to 0 for
all the supported buffer sizes, so FFA_RXTX_MAP is always called with an
invalid page count.

Example: with rxtx_bufsz = 4K, the expression becomes 1 / 4096 on 4K/16K/64K
page kernel, so pg_cnt == 0. Wouldn’t this  cause a boot-time regression for
FF-A driver init ? Have you tested this ? I am trying to understand what I
might be missing here.

-- 
Regards,
Sudeep