linux-kernel - Re: [PATCH v3] mmc: mtk-sd: reduce CIT for better performance

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Message-ID: <47ee4c8b-dedf-d69a-dceb-dcaa34ddd0e1@collabora.com>
Date:   Mon, 5 Jun 2023 10:48:10 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Wenbin Mei <wenbin.mei@...iatek.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Chaotian Jing <chaotian.jing@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ritesh Harjani <riteshh@...eaurora.org>,
        Asutosh Das <asutoshd@...eaurora.org>,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v3] mmc: mtk-sd: reduce CIT for better performance

Il 05/06/23 08:01, Wenbin Mei ha scritto:
> CQHCI_SSC1 indicates to CQE the polling period to use when using periodic
> SEND_QUEUE_STATUS(CMD13) polling.
> Since MSDC CQE uses msdc_hclk as ITCFVAL, so driver should use hclk
> frequency to get the actual time.
> The default value 0x1000 that corresponds to 150us for MediaTek SoCs, let's
> decrease it to 0x40 that corresponds to 2.35us, which can improve the
> performance of some eMMC devices.
> 
> Signed-off-by: Wenbin Mei <wenbin.mei@...iatek.com>

OK! That's almost good now. There's only one consideration here: if MediaTek
SoCs *require* msdc_hclk to calculate the CIT time, this means that this clock
is critical for CQHCI functionality.

If msdc_hclk is not present, CQHCI cannot work correctly... so you don't have
to cover the case in which there's no msdc_hclk clock: if that's not present,
either fail probing, or disable CQHCI.

> ---
>   drivers/mmc/host/cqhci.h  |  1 +
>   drivers/mmc/host/mtk-sd.c | 47 +++++++++++++++++++++++++++++++++++++++
>   2 files changed, 48 insertions(+)
> 
> diff --git a/drivers/mmc/host/cqhci.h b/drivers/mmc/host/cqhci.h
> index ba9387ed90eb..292b89ebd978 100644
> --- a/drivers/mmc/host/cqhci.h
> +++ b/drivers/mmc/host/cqhci.h
> @@ -23,6 +23,7 @@
>   /* capabilities */
>   #define CQHCI_CAP			0x04
>   #define CQHCI_CAP_CS			0x10000000 /* Crypto Support */
> +#define CQHCI_CAP_ITCFMUL(x)		(((x) & GENMASK(15, 12)) >> 12)
>   
>   /* configuration */
>   #define CQHCI_CFG			0x08
> diff --git a/drivers/mmc/host/mtk-sd.c b/drivers/mmc/host/mtk-sd.c
> index edade0e54a0c..c221ef8a6992 100644
> --- a/drivers/mmc/host/mtk-sd.c
> +++ b/drivers/mmc/host/mtk-sd.c
> @@ -473,6 +473,7 @@ struct msdc_host {
>   	struct msdc_tune_para def_tune_para; /* default tune setting */
>   	struct msdc_tune_para saved_tune_para; /* tune result of CMD21/CMD19 */
>   	struct cqhci_host *cq_host;
> +	u32 cq_ssc1_time;
>   };
>   
>   static const struct mtk_mmc_compatible mt2701_compat = {
> @@ -2450,9 +2451,50 @@ static void msdc_hs400_enhanced_strobe(struct mmc_host *mmc,
>   	}
>   }
>   
> +static void msdc_cqe_cit_cal(struct msdc_host *host, u64 timer_ns)

static int msdc_cqe_cit_cal(....)

> +{
> +	struct mmc_host *mmc = mmc_from_priv(host);
> +	struct cqhci_host *cq_host = mmc->cqe_private;
> +	u8 itcfmul;
> +	u32 hclk_freq;

hclk_freq should be `unsigned long`, as that's what clk_get_rate() returns.

> +	u64 value;
> +
> +	/* Since MSDC CQE uses msdc_hclk as ITCFVAL, so driver should use hclk
> +	 * frequency to get the actual time for CIT.
> +	 */

	/*
	 * On MediaTek SoCs the MSDC controller's CQE uses msdc_hclk as ITCFVAL
	 * so we multiply/divide the HCLK frequency by ITCFMUL to calculate the
	 * Send Status Command Idle Timer (CIT) value.
	 */
	if (!host->h_clk)
		return -EINVAL;

	hclk_freq = clk_get_rate(host->h_clk);
	itcfmul = CQHCI_CAP_ITFCMUL(cqhci_readl(cq_host, CQHCI_CAP));
	switch (itcfmul) {
		....
	}

> +	if (host->h_clk) {
> +		hclk_freq = clk_get_rate(host->h_clk);
> +		itcfmul = CQHCI_CAP_ITCFMUL(cqhci_readl(cq_host, CQHCI_CAP));
> +		switch (itcfmul) {
> +		case 0x0:
> +			do_div(hclk_freq, 1000);
> +			break;
> +		case 0x1:
> +			do_div(hclk_freq, 100);
> +			break;
> +		case 0x2:
> +			do_div(hclk_freq, 10);
> +			break;
> +		case 0x3:
> +			break;
> +		case 0x4:
> +			hclk_freq = hclk_freq * 10;
> +			break;
> +		default:
> +			host->cq_ssc1_time = 0x40;
> +			return;
> +		value = hclk_freq * timer_ns;
> +		do_div(value, 1000000000ULL);
> +		host->cq_ssc1_time = value;
> +	} else {
> +		host->cq_ssc1_time = 0x40;
> +	}
> +}
> +
>   static void msdc_cqe_enable(struct mmc_host *mmc)
>   {
>   	struct msdc_host *host = mmc_priv(mmc);
> +	struct cqhci_host *cq_host = mmc->cqe_private;
>   
>   	/* enable cmdq irq */
>   	writel(MSDC_INT_CMDQ, host->base + MSDC_INTEN);
> @@ -2462,6 +2504,9 @@ static void msdc_cqe_enable(struct mmc_host *mmc)
>   	msdc_set_busy_timeout(host, 20 * 1000000000ULL, 0);
>   	/* default read data timeout 1s */
>   	msdc_set_timeout(host, 1000000000ULL, 0);
> +
> +	/* Set the send status command idle timer */
> +	cqhci_writel(cq_host, host->cq_ssc1_time, CQHCI_SSC1);
>   }
>   
>   static void msdc_cqe_disable(struct mmc_host *mmc, bool recovery)
> @@ -2803,6 +2848,8 @@ static int msdc_drv_probe(struct platform_device *pdev)
>   		/* cqhci 16bit length */
>   		/* 0 size, means 65536 so we don't have to -1 here */
>   		mmc->max_seg_size = 64 * 1024;
> +		/* Reduce CIT to 0x40 that corresponds to 2.35us */
> +		msdc_cqe_cit_cal(host, 2350);

		ret = msdc_cqe_cit_cal(...)
		if (ret)
			goto release;

^^^^ either fail probe, or use the eMMC/SD without CQHCI support.

Regards,
Angelo

>   	}
>   
>   	ret = devm_request_irq(&pdev->dev, host->irq, msdc_irq,