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Date:   Wed, 14 Sep 2022 14:11:31 +0200
From:   Thierry Reding <thierry.reding@gmail.com>
To:     Prathamesh Shete <pshete@nvidia.com>
Cc:     adrian.hunter@intel.com, ulf.hansson@linaro.org,
        jonathanh@nvidia.com, p.zabel@pengutronix.de,
        linux-mmc@vger.kernel.org, linux-tegra@vger.kernel.org,
        linux-kernel@vger.kernel.org, anrao@nvidia.com,
        smangipudi@nvidia.com, kyarlagadda@nvidia.com
Subject: Re: [PATCH v2 2/4] mmc: sdhci-tegra: Add support to program MC
 streamID
Message-ID: <YyHE86HI43lPcQQr@orome>
References: <20220914095628.26093-1-pshete@nvidia.com>
 <20220914095628.26093-2-pshete@nvidia.com>
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On Wed, Sep 14, 2022 at 03:26:26PM +0530, Prathamesh Shete wrote:
> As per T23x MSS IAS SMMU clients are supposed

This reference isn't useful because this document is not available
publicly. If this information exists in the TRM, then make a reference
to that, otherwise just leave out the reference and keep the rest of the
comment.

> to program streamid from their respective address spaces instead of MC

s/streamid/stream ID/ to match the ARM SMMU spelling.

> override
> Define NVQUIRK_PROGRAM_MC_STREAMID and use it to program SMMU streamid
> from the SDMMC client address space

Maybe make this all look more like one big paragraph. Right now it looks
fragments of sentences thrown together and is difficult to read.

>=20
> Signed-off-by: Aniruddha TVS Rao <anrao@nvidia.com>
> Signed-off-by: Prathamesh Shete <pshete@nvidia.com>
> ---
>  drivers/mmc/host/sdhci-tegra.c | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
>=20
> diff --git a/drivers/mmc/host/sdhci-tegra.c b/drivers/mmc/host/sdhci-tegr=
a.c
> index a6c5bbae77b4..b66b0cc51497 100644
> --- a/drivers/mmc/host/sdhci-tegra.c
> +++ b/drivers/mmc/host/sdhci-tegra.c
> @@ -25,6 +25,7 @@
>  #include <linux/mmc/slot-gpio.h>
>  #include <linux/gpio/consumer.h>
>  #include <linux/ktime.h>
> +#include <linux/iommu.h>
> =20
>  #include <soc/tegra/common.h>
> =20
> @@ -94,6 +95,8 @@
>  #define SDHCI_TEGRA_AUTO_CAL_STATUS			0x1ec
>  #define SDHCI_TEGRA_AUTO_CAL_ACTIVE			BIT(31)
> =20
> +#define SDHCI_TEGRA_CIF2AXI_CTRL_0			0x1fc
> +
>  #define NVQUIRK_FORCE_SDHCI_SPEC_200			BIT(0)
>  #define NVQUIRK_ENABLE_BLOCK_GAP_DET			BIT(1)
>  #define NVQUIRK_ENABLE_SDHCI_SPEC_300			BIT(2)
> @@ -121,6 +124,7 @@
>  #define NVQUIRK_HAS_TMCLK				BIT(10)
> =20
>  #define NVQUIRK_HAS_ANDROID_GPT_SECTOR			BIT(11)
> +#define NVQUIRK_PROGRAM_MC_STREAMID			BIT(17)

Why is this called "program MC stream ID"? What's programmed is the SMMU
stream ID, right? Perhaps just leave out that MC_ prefix altogether
since there's no ambiguity with any other quirk to begin with.

Also, why skip from bit 11 (of the GPT sector quirk) to bit 17? Can we
not use bit 12 as the next one?

> =20
>  /* SDMMC CQE Base Address for Tegra Host Ver 4.1 and Higher */
>  #define SDHCI_TEGRA_CQE_BASE_ADDR			0xF000
> @@ -177,6 +181,7 @@ struct sdhci_tegra {
>  	bool enable_hwcq;
>  	unsigned long curr_clk_rate;
>  	u8 tuned_tap_delay;
> +	u32 streamid;
>  };
> =20
>  static u16 tegra_sdhci_readw(struct sdhci_host *host, int reg)
> @@ -1564,6 +1569,7 @@ static const struct sdhci_tegra_soc_data soc_data_t=
egra234 =3D {
>  		    NVQUIRK_DIS_CARD_CLK_CONFIG_TAP |
>  		    NVQUIRK_ENABLE_SDR50 |
>  		    NVQUIRK_ENABLE_SDR104 |
> +		    NVQUIRK_PROGRAM_MC_STREAMID |
>  		    NVQUIRK_HAS_TMCLK,
>  	.min_tap_delay =3D 95,
>  	.max_tap_delay =3D 111,
> @@ -1637,6 +1643,7 @@ static int sdhci_tegra_probe(struct platform_device=
 *pdev)
>  	struct sdhci_pltfm_host *pltfm_host;
>  	struct sdhci_tegra *tegra_host;
>  	struct clk *clk;
> +	struct iommu_fwspec *fwspec;

The above is largely sorted in reverse christmas tree order, so this one
sticks out a bit. Maybe put it before the clk declaration. Not usually a
big deal, really, but since you're going to touch this anyway, may as
well touch that up.

>  	int rc;
> =20
>  	soc_data =3D of_device_get_match_data(&pdev->dev);
> @@ -1775,6 +1782,23 @@ static int sdhci_tegra_probe(struct platform_devic=
e *pdev)
>  	if (rc)
>  		goto err_add_host;
> =20
> +	/* Program MC streamID for DMA transfers */
> +	if (soc_data->nvquirks & NVQUIRK_PROGRAM_MC_STREAMID) {
> +		fwspec =3D dev_iommu_fwspec_get(&pdev->dev);
> +		if (fwspec =3D=3D NULL) {
> +			rc =3D -ENODEV;
> +			dev_err(mmc_dev(host->mmc),
> +				"failed to get MC streamid: %d\n",
> +				rc);
> +			goto err_rst_get;

Do we really want to make this fatal? What if somebody really wants to
not put the SD/MMC controllers behind an IOMMU? It's quite unlikely to
happen, but it's technically possible.

Also, there was a brief time where the DTS files didn't have any iommus
properties, so if somebody were to use a DTS from that era and a kernel
with this patch applied, they'd end up with non-functional SD/MMC.
Again, that's very unlikely to happen, but it could, if for example this
patch ends up being back-ported or something like that.

I think it's safe (and easier) to ignore this case. Perhaps if you
really want people to use SD/MMC you may want to add a warning here
instead. But even that shouldn't be necessary. If the stream ID is not
programmed as required, the SMMU should fault and give people the hint
that they need to fix this.

> +		} else {
> +			tegra_host->streamid =3D fwspec->ids[0] & 0xffff;
> +			tegra_sdhci_writel(host, tegra_host->streamid |
> +						(tegra_host->streamid << 8),
> +						SDHCI_TEGRA_CIF2AXI_CTRL_0);

Perhaps define macros for the read/write stream ID fields in this
register? Otherwise it might be confusing why you're writing the value
twice.

Thierry

> +		}
> +	}
> +
>  	return 0;
> =20
>  err_add_host:
> @@ -1861,6 +1885,8 @@ static int sdhci_tegra_suspend(struct device *dev)
>  static int sdhci_tegra_resume(struct device *dev)
>  {
>  	struct sdhci_host *host =3D dev_get_drvdata(dev);
> +	struct sdhci_pltfm_host *pltfm_host =3D sdhci_priv(host);
> +	struct sdhci_tegra *tegra_host =3D sdhci_pltfm_priv(pltfm_host);
>  	int ret;
> =20
>  	ret =3D mmc_gpio_set_cd_wake(host->mmc, false);
> @@ -1871,6 +1897,13 @@ static int sdhci_tegra_resume(struct device *dev)
>  	if (ret)
>  		return ret;
> =20
> +	/* Re-program MC streamID for DMA transfers */
> +	if (tegra_host->soc_data->nvquirks & NVQUIRK_PROGRAM_MC_STREAMID) {
> +		tegra_sdhci_writel(host, tegra_host->streamid |
> +					(tegra_host->streamid << 8),
> +					SDHCI_TEGRA_CIF2AXI_CTRL_0);
> +	}
> +
>  	ret =3D sdhci_resume_host(host);
>  	if (ret)
>  		goto disable_clk;
> --=20
> 2.17.1
>=20

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