linux-kernel - Re: [PATCH v4] mmc: mtk-sd: reduce CIT for better performance

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Date:   Tue, 6 Jun 2023 09:46:01 +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 v4] mmc: mtk-sd: reduce CIT for better performance

Il 05/06/23 14:14, 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>
> ---
>   drivers/mmc/host/cqhci.h  |  1 +
>   drivers/mmc/host/mtk-sd.c | 45 +++++++++++++++++++++++++++++++++++++++
>   2 files changed, 46 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..9f540973caff 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 +2451,48 @@ static void msdc_hs400_enhanced_strobe(struct mmc_host *mmc,
>   	}
>   }
>   
> +static void msdc_cqe_cit_cal(struct msdc_host *host, u64 timer_ns)
> +{
> +	struct mmc_host *mmc = mmc_from_priv(host);
> +	struct cqhci_host *cq_host = mmc->cqe_private;
> +	u8 itcfmul;
> +	u64 hclk_freq;
> +	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.
      */

The proposed comment increases readability.

Cheers,
Angelo