linux-kernel - Re: [PATCH 2/3] mmc: meson-gx: add ddr-access-quirk

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Date:   Mon, 13 May 2019 10:47:45 -0700
From:   Kevin Hilman <khilman@...libre.com>
To:     Neil Armstrong <narmstrong@...libre.com>, ulf.hansson@...aro.org
Cc:     baylibre-upstreaming@...ups.io,
        Neil Armstrong <narmstrong@...libre.com>,
        linux-mmc@...r.kernel.org, linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mmc: meson-gx: add ddr-access-quirk

Neil Armstrong <narmstrong@...libre.com> writes:

> On the Amlogic G12A SoC family, (only) the SDIO controller fails to access
> the data from DDR, leading to a broken controller.
>
> But each MMC controller has 1,5KiB of SRAM after the registers, that can
> be used as bounce buffer to avoid direct DDR access from the integrated
> DMAs (this SRAM may be used by the boot ROM when DDR is not yet initialized).
>
> The quirk is to disable the chained descriptor for this controller, and
> use this SRAM memory zone as buffer for the bounce buffer fallback mode.
>
> The performance hit hasn't been evaluated, but the fix has been tested
> using a WiFi AP6398S SDIO module, and the iperf3 Bandwidth measurement gave
> 55.2 Mbits/sec over a 63 Hours long test, with the SDIO ios set as High-Speed
> at 50MHz clock. It gave 170 Mbits/sec as SDR104 and 200MHz clock.
>
> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>

Reviewed-by: Kevin Hilman <khilman@...libre.com>