Re: [PATCH v3 3/3] mmc: xenon: Fix 2G limitation on AC5 SoC

[Adrian Hunter]

On 5/12/22 12:59, Vadym Kochan wrote:
> There is a limitation on AC5 SoC that mmc controller
> can't have DMA access over 2G memory, so use SDMA with
> a bounce buffer. Swiotlb can't help because on arm64 arch
> it reserves memblock's at the end of the memory.
> 
> Additionally set mask to 34 bit since on AC5 SoC RAM starts
> at 0x2_00000000.

Can you explain more about how a 34-bit DMA mask works when
SDMA only supports 32-bit addresses?

> 
> Co-developed-by: Elad Nachman <enachman@xxxxxxxxxxx>
> Signed-off-by: Elad Nachman <enachman@xxxxxxxxxxx>
> Signed-off-by: Vadym Kochan <vadym.kochan@xxxxxxxxxxx>
> ---
>  drivers/mmc/host/sdhci-xenon.c | 38 ++++++++++++++++++++++++++++++++++
>  drivers/mmc/host/sdhci-xenon.h |  3 ++-
>  2 files changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/sdhci-xenon.c b/drivers/mmc/host/sdhci-xenon.c
> index 08e838400b52..5f3db0425674 100644
> --- a/drivers/mmc/host/sdhci-xenon.c
> +++ b/drivers/mmc/host/sdhci-xenon.c
> @@ -13,7 +13,9 @@
>  
>  #include <linux/acpi.h>
>  #include <linux/delay.h>
> +#include <linux/dma-mapping.h>
>  #include <linux/ktime.h>
> +#include <linux/mm.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
>  #include <linux/pm.h>
> @@ -253,6 +255,22 @@ static unsigned int xenon_get_max_clock(struct sdhci_host *host)
>  		return pltfm_host->clock;
>  }
>  
> +static int xenon_set_dma_mask(struct sdhci_host *host)
> +{
> +	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
> +	struct xenon_priv *priv = sdhci_pltfm_priv(pltfm_host);
> +	struct mmc_host *mmc = host->mmc;
> +	struct device *dev = mmc_dev(mmc);
> +
> +	if (priv->hw_version == XENON_AC5) {
> +		host->flags &= ~SDHCI_USE_64_BIT_DMA;
> +
> +		return dma_set_mask_and_coherent(dev, DMA_BIT_MASK(34));
> +	}
> +
> +	return sdhci_set_dma_mask(host);
> +}
> +
>  static const struct sdhci_ops sdhci_xenon_ops = {
>  	.voltage_switch		= xenon_voltage_switch,
>  	.set_clock		= sdhci_set_clock,
> @@ -261,6 +279,7 @@ static const struct sdhci_ops sdhci_xenon_ops = {
>  	.reset			= xenon_reset,
>  	.set_uhs_signaling	= xenon_set_uhs_signaling,
>  	.get_max_clock		= xenon_get_max_clock,
> +	.set_dma_mask		= xenon_set_dma_mask,
>  };
>  
>  static const struct sdhci_pltfm_data sdhci_xenon_pdata = {
> @@ -486,6 +505,18 @@ static void xenon_sdhc_unprepare(struct sdhci_host *host)
>  	xenon_disable_sdhc(host, sdhc_id);
>  }
>  
> +static int xenon_ac5_probe(struct sdhci_host *host)
> +{
> +	struct sysinfo si;
> +
> +	si_meminfo(&si);
> +
> +	if ((si.totalram * si.mem_unit) > SZ_2G)
> +		host->quirks |= SDHCI_QUIRK_BROKEN_ADMA;
> +
> +	return 0;
> +}
> +
>  static int xenon_probe(struct platform_device *pdev)
>  {
>  	struct sdhci_pltfm_host *pltfm_host;
> @@ -533,6 +564,12 @@ static int xenon_probe(struct platform_device *pdev)
>  		}
>  	}
>  
> +	if (priv->hw_version == XENON_AC5) {
> +		err = xenon_ac5_probe(host);
> +		if (err)
> +			goto err_clk_axi;
> +	}
> +
>  	err = mmc_of_parse(host->mmc);
>  	if (err)
>  		goto err_clk_axi;
> @@ -682,6 +719,7 @@ static const struct of_device_id sdhci_xenon_dt_ids[] = {
>  	{ .compatible = "marvell,armada-ap807-sdhci", .data = (void *)XENON_AP807},
>  	{ .compatible = "marvell,armada-cp110-sdhci", .data =  (void *)XENON_CP110},
>  	{ .compatible = "marvell,armada-3700-sdhci", .data =  (void *)XENON_A3700},
> +	{ .compatible = "marvell,ac5-sdhci", .data = (void *)XENON_AC5},
>  	{}
>  };
>  MODULE_DEVICE_TABLE(of, sdhci_xenon_dt_ids);
> diff --git a/drivers/mmc/host/sdhci-xenon.h b/drivers/mmc/host/sdhci-xenon.h
> index 3e9c6c908a79..0460d97aad26 100644
> --- a/drivers/mmc/host/sdhci-xenon.h
> +++ b/drivers/mmc/host/sdhci-xenon.h
> @@ -57,7 +57,8 @@ enum xenon_variant {
>  	XENON_A3700,
>  	XENON_AP806,
>  	XENON_AP807,
> -	XENON_CP110
> +	XENON_CP110,
> +	XENON_AC5
>  };
>  
>  struct xenon_priv {