Date: Thu, 1 Feb 2024 13:24:34 -0600
From: Andrew Davis <afd@...com>
To: Judith Mendez <jm@...com>, Ulf Hansson <ulf.hansson@...aro.org>
CC: Adrian Hunter <adrian.hunter@...el.com>, <linux-mmc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Randolph Sapp <rs@...com>,
        Vignesh
 Raghavendra <vigneshr@...com>
Subject: Re: [PATCH v1 1/5] mmc: sdhci_am654: Add tuning algorithm for delay
 chain

On 1/31/24 3:50 PM, Judith Mendez wrote:
> Currently the sdhci_am654 driver only supports one tuning
> algorithm which should be used only when DLL is enabled. The
> ITAPDLY is selected from the largest passing window and the
> buffer is viewed as a circular buffer.
> 
> The new algorithm should be used when the delay chain
> is enabled. The ITAPDLY is selected from the largest passing
> window and the buffer is not viewed as a circular buffer.
> 
> This implementation is based off of the following paper: [1].
> 
> Also add support for multiple failing windows.
> 
> [1] https://www.ti.com/lit/an/spract9/spract9.pdf
> 
> Fixes: 13ebeae68ac9 ("mmc: sdhci_am654: Add support for software tuning")
> Signed-off-by: Judith Mendez <jm@...com>
> ---
>   drivers/mmc/host/sdhci_am654.c | 128 +++++++++++++++++++++++++++------
>   1 file changed, 108 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci_am654.c b/drivers/mmc/host/sdhci_am654.c
> index d659c59422e1..a3798c9912f6 100644
> --- a/drivers/mmc/host/sdhci_am654.c
> +++ b/drivers/mmc/host/sdhci_am654.c
> @@ -149,10 +149,17 @@ struct sdhci_am654_data {
>   	int strb_sel;
>   	u32 flags;
>   	u32 quirks;
> +	bool dll_enable;
>   
>   #define SDHCI_AM654_QUIRK_FORCE_CDTEST BIT(0)
>   };
>   
> +struct window {
> +	u8 start;
> +	u8 end;
> +	u8 length;
> +};
> +
>   struct sdhci_am654_driver_data {
>   	const struct sdhci_pltfm_data *pdata;
>   	u32 flags;
> @@ -290,10 +297,13 @@ static void sdhci_am654_set_clock(struct sdhci_host *host, unsigned int clock)
>   
>   	regmap_update_bits(sdhci_am654->base, PHY_CTRL4, mask, val);
>   
> -	if (timing > MMC_TIMING_UHS_SDR25 && clock >= CLOCK_TOO_SLOW_HZ)
> +	if (timing > MMC_TIMING_UHS_SDR25 && clock >= CLOCK_TOO_SLOW_HZ) {
>   		sdhci_am654_setup_dll(host, clock);
> -	else
> +		sdhci_am654->dll_enable = true;
> +	} else {
>   		sdhci_am654_setup_delay_chain(sdhci_am654, timing);
> +		sdhci_am654->dll_enable = false;
> +	}
>   
>   	regmap_update_bits(sdhci_am654->base, PHY_CTRL5, CLKBUFSEL_MASK,
>   			   sdhci_am654->clkbuf_sel);
> @@ -408,39 +418,117 @@ static u32 sdhci_am654_cqhci_irq(struct sdhci_host *host, u32 intmask)
>   	return 0;
>   }
>   
> -#define ITAP_MAX	32
> +#define ITAPDLY_LENGTH 32
> +#define ITAPDLY_LAST_INDEX 31
> +static u32 sdhci_am654_calculate_itap(struct sdhci_host *host, struct window
> +			  *fail_window, u8 num_fails, bool circular_buffer)
> +{
> +	struct device *dev = mmc_dev(host->mmc);
> +	struct window pass_window, first_fail, last_fail;

struct window pass_window = {}, ..

Then you can drop the memset()s below.

> +	u8 itap = 0, start_fail = 0, end_fail = 0, pass_length = 0;
> +	int prev_end_fail = -1;
> +	u8 i;
> +
> +	memset(&pass_window, 0, sizeof(pass_window));
> +	memset(&first_fail, 0, sizeof(first_fail));
> +	memset(&last_fail, 0, sizeof(last_fail));
> +
> +	if (!num_fails) {
> +		itap = ITAPDLY_LAST_INDEX >> 1;

return ITAPDLY_LAST_INDEX >> 1;

> +	} else if (fail_window->length == ITAPDLY_LENGTH) {
> +		dev_err(dev, "No passing ITAPDLY, return 0\n");
> +		itap = 0;

return 0;

> +	} else {

If you shortcut return directly in the above to branches, then
this all below doesn't need to be in the else {} and you won't
have to indent it all out so far.

> +		for (i = 0; i < num_fails; i++) {
> +			start_fail = fail_window[i].start;
> +			end_fail = fail_window[i].end;
> +
> +			if (i == 0) {

Move this first case to before the loop, we already know what
first_fail will be filled with. No need to check i == 0 every iteration
of the loop. Same for last_fail, just move to after the loop.

> +				first_fail.start = start_fail;
> +				first_fail.end = end_fail;
> +				first_fail.length = fail_window[0].length;
> +			}
> +
> +			if (i == num_fails - 1) {
> +				last_fail.start = start_fail;
> +				last_fail.end = end_fail;
> +				last_fail.length = fail_window[i].length;
> +			}
> +
> +			pass_length = start_fail - (prev_end_fail + 1);
> +			if (pass_length > pass_window.length) {
> +				pass_window.start = prev_end_fail + 1;
> +				pass_window.length = pass_length;
> +			}
> +			prev_end_fail = end_fail;
> +		}
> +
> +		if (!circular_buffer) {
> +			if (ITAPDLY_LAST_INDEX - end_fail > pass_window.length) {
> +				pass_window.start = end_fail + 1;
> +				pass_window.length = ITAPDLY_LAST_INDEX - end_fail;
> +			}
> +		} else {
> +			pass_length = ITAPDLY_LAST_INDEX - end_fail + first_fail.start;
> +			if (pass_length > pass_window.length) {
> +				pass_window.start = last_fail.end + 1;
> +				pass_window.length = pass_length;
> +			}
> +		}
> +
> +		if (!circular_buffer)
> +			itap = pass_window.start + (pass_window.length >> 1);
> +		else
> +			itap = (pass_window.start + (pass_window.length >> 1)) % ITAPDLY_LENGTH;
> +
> +		if (itap < 0 || itap > ITAPDLY_LAST_INDEX)
> +			itap = 0;
> +	}
> +
> +	return itap;
> +}
> +
>   static int sdhci_am654_platform_execute_tuning(struct sdhci_host *host,
>   					       u32 opcode)
>   {
>   	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
>   	struct sdhci_am654_data *sdhci_am654 = sdhci_pltfm_priv(pltfm_host);
> -	int cur_val, prev_val = 1, fail_len = 0, pass_window = 0, pass_len;
> -	u32 itap;
> +	struct window fail_window[ITAPDLY_LENGTH];
> +	u8 prev_pass = 1;
> +	u8 fail_index = 0;
> +	u8 curr_pass, itap;
> +
> +	memset(fail_window, 0, sizeof(fail_window[0]) * ITAPDLY_LENGTH);
>   
>   	/* Enable ITAPDLY */
>   	regmap_update_bits(sdhci_am654->base, PHY_CTRL4, ITAPDLYENA_MASK,
>   			   1 << ITAPDLYENA_SHIFT);
>   
> -	for (itap = 0; itap < ITAP_MAX; itap++) {
> +	for (itap = 0; itap < ITAPDLY_LENGTH; itap++) {
>   		sdhci_am654_write_itapdly(sdhci_am654, itap);
>   
> -		cur_val = !mmc_send_tuning(host->mmc, opcode, NULL);
> -		if (cur_val && !prev_val)
> -			pass_window = itap;
> +		curr_pass = !mmc_send_tuning(host->mmc, opcode, NULL);
>   
> -		if (!cur_val)
> -			fail_len++;
> +		if (!curr_pass && prev_pass)
> +			fail_window[fail_index].start = itap;
>   
> -		prev_val = cur_val;
> +		if (!curr_pass) {
> +			fail_window[fail_index].end = itap;
> +			fail_window[fail_index].length++;
> +		}
> +
> +		if (curr_pass && !prev_pass)
> +			fail_index++;
> +
> +		prev_pass = curr_pass;
>   	}
> -	/*
> -	 * Having determined the length of the failing window and start of
> -	 * the passing window calculate the length of the passing window and
> -	 * set the final value halfway through it considering the range as a
> -	 * circular buffer
> -	 */
> -	pass_len = ITAP_MAX - fail_len;
> -	itap = (pass_window + (pass_len >> 1)) % ITAP_MAX;
> +
> +	if (fail_window[fail_index].length != 0)
> +		fail_index++;
> +
> +	itap = sdhci_am654_calculate_itap(host, fail_window, fail_index,
> +					  (sdhci_am654->dll_enable ? true : false));

dll_enable is already a bool, the line:

(sdhci_am654->dll_enable ? true : false)

has no effect, just use sdhci_am654->dll_enable directly.

Andrew

> +
>   	sdhci_am654_write_itapdly(sdhci_am654, itap);
>   
>   	return 0;

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