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SubjectRe: [RFC] i.MX25/35/SDHCI: switch off DMA usage
On Fri, Mar 27, 2015 at 11:52:04AM +0100, Juergen Borleis wrote:
> DMA and the required overhead on very small data blocks seems an expensive
> operation. Due to erratum ENGCM07207 for i.MX25 and i.MX35 SoCs the
> support for multiblock transfers is disabled which results into a huge
> amount of single 512 byte sector transfers and interrupts. This slows down
> the transmission speed to below 500 kiB/s (even at 50 MHz SD card clock).
> Using PIO instead of DMA to avoid ENGCM07207 happens and re-enabling
> multiblock transfers again improve the transmission capability up to about
> 2.5 MiB/s.
>
> I'm still not sure if ENGCM07207 is related to DMA only and can not happen
> when PIO is used instead. Someone out there with experience regarding this
> topic?

The errata does not state it's related to DMA only.
http://cache.freescale.com/files/dsp/doc/errata/IMX35CE.pdf
I could double check with our IC guys to confirm it.

Regards
Dong Aisheng

> ---
> drivers/mmc/host/sdhci-esdhc-imx.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-esdhc-imx.c
> index 10ef8244a239..f5fd569a17c3 100644
> --- a/drivers/mmc/host/sdhci-esdhc-imx.c
> +++ b/drivers/mmc/host/sdhci-esdhc-imx.c
> @@ -976,8 +976,8 @@ static int sdhci_esdhc_imx_probe(struct platform_device *pdev)
>
> if (imx_data->socdata->flags & ESDHC_FLAG_ENGCM07207)
> /* Fix errata ENGcm07207 present on i.MX25 and i.MX35 */
> - host->quirks |= SDHCI_QUIRK_NO_MULTIBLOCK
> - | SDHCI_QUIRK_BROKEN_ADMA;
> + host->quirks |=
> + SDHCI_QUIRK_BROKEN_ADMA | SDHCI_QUIRK_BROKEN_DMA;
>
> /*
> * The imx6q ROM code will change the default watermark level setting
> --
> 1.7.10.4
>
> Juergen


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