Re: [PATCH] mmc: mediatek: Add cmd polling mode

[Chaotian Jing]

On Mon, 2022-01-24 at 20:18 +0800, Derong Liu wrote:
> We found sdcard can gain more read/write performance
> when using cmd polling mode instead of interrupt mode, in the
> meantime,
> there are much more devices have equipped with high frequency cpu,
> so it is necessary to support cmd polling mode.
> 
Hi, I think you have not found the root cause of performace drop. if
the sdcard read/write performance is 100MB/s, which means that it can
complete 512KB of data xfer within 5ms, and if performance drop is 5%,
then means that your interrupt mode will take more than 250us.
Is it possible to clarify if the interrupt mode really takes 250us?

And, if you find that the polling mode is readlly fast then interrupt
mode and has no side effect(ie. cpu loading issue), then, We will drop
the interrupt mode of waiting response.
> Signed-off-by: Derong Liu <derong.liu@xxxxxxxxxxxx>
> ---
>  drivers/mmc/host/mtk-sd.c | 92 +++++++++++++++++++++++++++++++++++
> ----
>  1 file changed, 83 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/mmc/host/mtk-sd.c b/drivers/mmc/host/mtk-sd.c
> index 65037e1d7723..612f5115ca4b 100644
> --- a/drivers/mmc/host/mtk-sd.c
> +++ b/drivers/mmc/host/mtk-sd.c
> @@ -465,6 +465,7 @@ struct msdc_host {
>  	bool hs400_tuning;	/* hs400 mode online tuning */
>  	bool internal_cd;	/* Use internal card-detect logic */
>  	bool cqhci;		/* support eMMC hw cmdq */
> +	bool cmd_polling_mode;	/* support cmd polling mode */
>  	struct msdc_save_para save_para; /* used when gate HCLK */
>  	struct msdc_tune_para def_tune_para; /* default tune setting */
>  	struct msdc_tune_para saved_tune_para; /* tune result of
> CMD21/CMD19 */
> @@ -1250,6 +1251,63 @@ static inline bool msdc_cmd_is_ready(struct
> msdc_host *host,
>  	return true;
>  }
>  
> +static inline int use_cmd_polling_mode(struct msdc_host *host,
> +	struct mmc_command *cmd)
> +{
> +	/* R1B use interrupt mode */
> +	return (host->cmd_polling_mode &&
> +			((mmc_from_priv(host))->caps2 &
> MMC_CAP2_NO_SDIO) &&
> +			(mmc_resp_type(cmd) != MMC_RSP_R1B));
> +}
> +
> +static bool msdc_command_resp_polling(struct msdc_host *host,
> +	struct mmc_request *mrq, struct mmc_command *cmd,
> +	unsigned long timeout)
> +{
> +	bool ret = false;
> +	unsigned long tmo;
> +	int events;
> +	unsigned long flags;
> +
> +	if (!use_cmd_polling_mode(host, cmd))
> +		goto exit;
> +
> +retry:
> +	tmo = jiffies + timeout;
> +	while (1) {
> +		spin_lock_irqsave(&host->lock, flags);
why need spin lock ? if there are no SDIO device irq, then there is no
race conditon of access MSDC register.
> +		events = readl(host->base + MSDC_INT);
> +		if (events & cmd_ints_mask) {
> +			/* clear all int flag */
> +			events &= cmd_ints_mask;
> +			writel(events, host->base + MSDC_INT);
> +			spin_unlock_irqrestore(&host->lock, flags);
> +			break;
> +		}
> +		spin_unlock_irqrestore(&host->lock, flags);
> +
> +		if (time_after(jiffies, tmo) &&
> +			((events & cmd_ints_mask) == 0)) {
> +			dev_info(host->dev, "[%s]: CMD<%d>
> polling_for_completion timeout ARG<0x%.8x>\n",
> +				__func__, cmd->opcode, cmd->arg);
> +			ret = msdc_cmd_done(host, MSDC_INT_CMDTMO, mrq,
> cmd);
> +			goto exit;
> +		}
> +	}
> +
> +	if (cmd) {
> +		ret = msdc_cmd_done(host, events, mrq, cmd);
> +		/* if only autocmd23 done,
> +		 * it needs to polling the continue read/write cmd
> directly.
> +		 */
> +		if (!ret)
> +			goto retry;
> +	}
> +
> +exit:
> +	return ret;
> +}
> +
>  static void msdc_start_command(struct msdc_host *host,
>  		struct mmc_request *mrq, struct mmc_command *cmd)
>  {
> @@ -1273,7 +1331,10 @@ static void msdc_start_command(struct
> msdc_host *host,
>  	rawcmd = msdc_cmd_prepare_raw_cmd(host, mrq, cmd);
>  
>  	spin_lock_irqsave(&host->lock, flags);
> -	sdr_set_bits(host->base + MSDC_INTEN, cmd_ints_mask);
> +	if (use_cmd_polling_mode(host, cmd))
> +		sdr_clr_bits(host->base + MSDC_INTEN, cmd_ints_mask);
> +	else
> +		sdr_set_bits(host->base + MSDC_INTEN, cmd_ints_mask);
>  	spin_unlock_irqrestore(&host->lock, flags);
>  
>  	writel(cmd->arg, host->base + SDC_ARG);
> @@ -1290,9 +1351,11 @@ static void msdc_cmd_next(struct msdc_host
> *host,
>  	       host->hs400_tuning))) ||
>  	    (mrq->sbc && mrq->sbc->error))
>  		msdc_request_done(host, mrq);
> -	else if (cmd == mrq->sbc)
> +	else if (cmd == mrq->sbc) {
>  		msdc_start_command(host, mrq, mrq->cmd);
> -	else if (!cmd->data)
> +		msdc_command_resp_polling(host, mrq,
> +				mrq->cmd, CMD_TIMEOUT);
> +	} else if (!cmd->data)
>  		msdc_request_done(host, mrq);
>  	else
>  		msdc_start_data(host, cmd, cmd->data);
> @@ -1314,10 +1377,15 @@ static void msdc_ops_request(struct mmc_host
> *mmc, struct mmc_request *mrq)
>  	 * use HW option,  otherwise use SW option
>  	 */
>  	if (mrq->sbc && (!mmc_card_mmc(mmc->card) ||
> -	    (mrq->sbc->arg & 0xFFFF0000)))
> +	    (mrq->sbc->arg & 0xFFFF0000))) {
>  		msdc_start_command(host, mrq, mrq->sbc);
> -	else
> +		msdc_command_resp_polling(host, mrq,
> +				mrq->sbc, CMD_TIMEOUT);
> +	} else {
>  		msdc_start_command(host, mrq, mrq->cmd);
> +		msdc_command_resp_polling(host, mrq,
> +				mrq->cmd, CMD_TIMEOUT);
> +	}
>  }
>  
>  static void msdc_pre_req(struct mmc_host *mmc, struct mmc_request
> *mrq)
> @@ -1350,9 +1418,11 @@ static void msdc_post_req(struct mmc_host
> *mmc, struct mmc_request *mrq,
>  static void msdc_data_xfer_next(struct msdc_host *host, struct
> mmc_request *mrq)
>  {
>  	if (mmc_op_multi(mrq->cmd->opcode) && mrq->stop && !mrq->stop-
> >error &&
> -	    !mrq->sbc)
> +	    !mrq->sbc) {
>  		msdc_start_command(host, mrq, mrq->stop);
> -	else
> +		msdc_command_resp_polling(host, mrq,
> +				mrq->stop, CMD_TIMEOUT);
> +	} else
>  		msdc_request_done(host, mrq);
>  }
>  
> @@ -2492,11 +2562,15 @@ static void msdc_of_property_parse(struct
> platform_device *pdev,
>  	else
>  		host->hs400_cmd_resp_sel_rising = false;
>  
> -	if (of_property_read_bool(pdev->dev.of_node,
> -				  "supports-cqe"))
> +	if (of_property_read_bool(pdev->dev.of_node, "supports-cqe"))
>  		host->cqhci = true;
>  	else
>  		host->cqhci = false;
> +
> +	if (of_property_read_bool(pdev->dev.of_node, "mediatek,cmd-
> polling-mode"))
> +		host->cmd_polling_mode = true;
> +	else
> +		host->cmd_polling_mode = false;
>  }
>  
>  static int msdc_of_clock_parse(struct platform_device *pdev,