Subject: Re: [PATCH] soc: qcom: ipa: kill IPA_RX_BUFFER_ORDER

From: Bjorn Andersson <[email-masked]>
Date: Fri, 20 Mar 2020 12:11:07 -0700

On Fri 20 Mar 09:02 PDT 2020, Alex Elder wrote:

> Don't assume the receive buffer size is a power-of-2 number of pages.
> Instead, define the receive buffer size independently, and then
> compute the page order from that size when needed.
> 
> This fixes a build problem that arises when the ARM64_PAGE_SHIFT
> config option is set to have a page size greater than 4KB.  The
> problem was identified by Linux Kernel Functional Testing.
> 
> The IPA code basically assumed the page size to be 4KB.  A larger page
> size caused the receive buffer size to become correspondingly larger
> (32KB or 128KB for ARM64_16K_PAGES and ARM64_64K_PAGES, respectively).
> The receive buffer size is used to compute an "aggregation byte limit"
> value that gets programmed into the hardware, and the large page sizes
> caused that limit value to be too big to fit in a 5 bit field.  This
> triggered a BUILD_BUG_ON() call in ipa_endpoint_validate_build().
> 
> This fix causes a lot of receive buffer memory to be wasted if
> system is configured for page size greater than 4KB.  But such a
> misguided configuration will now build successfully.
> 
> Reported-by: Naresh Kamboju <[email-masked]>
> Signed-off-by: Alex Elder <[email-masked]>

Seems better than relying on PAGE_SIZE.

Reviewed-by: Bjorn Andersson <[email-masked]>

Regards,
Bjorn

> ---
> 
> Dave, I *hope* this is it for IPA for this release.	-Alex
> 
>  drivers/net/ipa/ipa_endpoint.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ipa/ipa_endpoint.c b/drivers/net/ipa/ipa_endpoint.c
> index 217cbf337ad7..6de03be28784 100644
> --- a/drivers/net/ipa/ipa_endpoint.c
> +++ b/drivers/net/ipa/ipa_endpoint.c
> @@ -26,8 +26,8 @@
>  
>  #define IPA_REPLENISH_BATCH	16
>  
> -#define IPA_RX_BUFFER_SIZE	(PAGE_SIZE << IPA_RX_BUFFER_ORDER)
> -#define IPA_RX_BUFFER_ORDER	1	/* 8KB endpoint RX buffers (2 pages) */
> +/* RX buffer is 1 page (or a power-of-2 contiguous pages) */
> +#define IPA_RX_BUFFER_SIZE	8192	/* PAGE_SIZE > 4096 wastes a LOT */
>  
>  /* The amount of RX buffer space consumed by standard skb overhead */
>  #define IPA_RX_BUFFER_OVERHEAD	(PAGE_SIZE - SKB_MAX_ORDER(NET_SKB_PAD, 0))
> @@ -758,7 +758,7 @@ static int ipa_endpoint_replenish_one(struct ipa_endpoint *endpoint)
>  	u32 len;
>  	int ret;
>  
> -	page = dev_alloc_pages(IPA_RX_BUFFER_ORDER);
> +	page = dev_alloc_pages(get_order(IPA_RX_BUFFER_SIZE));
>  	if (!page)
>  		return -ENOMEM;
>  
> @@ -787,7 +787,7 @@ static int ipa_endpoint_replenish_one(struct ipa_endpoint *endpoint)
>  err_trans_free:
>  	gsi_trans_free(trans);
>  err_free_pages:
> -	__free_pages(page, IPA_RX_BUFFER_ORDER);
> +	__free_pages(page, get_order(IPA_RX_BUFFER_SIZE));
>  
>  	return -ENOMEM;
>  }
> @@ -1073,7 +1073,7 @@ void ipa_endpoint_trans_release(struct ipa_endpoint *endpoint,
>  		struct page *page = trans->data;
>  
>  		if (page)
> -			__free_pages(page, IPA_RX_BUFFER_ORDER);
> +			__free_pages(page, get_order(IPA_RX_BUFFER_SIZE));
>  	}
>  }
>  
> -- 
> 2.20.1
>