netdev - Re: [PATCH] soc: qcom: ipa: kill IPA_RX_BUFFER

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Date:   Sat, 21 Mar 2020 19:47:13 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     elder@...aro.org
Cc:     bjorn.andersson@...aro.org, naresh.kamboju@...aro.org,
        netdev@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] soc: qcom: ipa: kill IPA_RX_BUFFER_ORDER

From: Alex Elder <elder@...aro.org>
Date: Fri, 20 Mar 2020 11:02:20 -0500

> 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 <naresh.kamboju@...aro.org>
> Signed-off-by: Alex Elder <elder@...aro.org>
> ---
> 
> Dave, I *hope* this is it for IPA for this release.	-Alex

Applied to net-next, thanks.