Date: Tue, 20 Feb 2024 14:10:20 -0600
From: Judith Mendez <jm@...com>
To: Adrian Hunter <adrian.hunter@...el.com>
CC: <linux-mmc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Ulf Hansson
	<ulf.hansson@...aro.org>
Subject: Re: [PATCH v2 1/7] mmc: sdhci_am654: Add tuning algorithm for delay
 chain


Hi Adrian,

On 2/16/24 11:09 AM, Adrian Hunter wrote:
> On 7/02/24 03:15, 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>
>> ---
>> Changelog:
>> v1->v2:
>> - Remove unnecessary indentations and if/else in
>>   sdhci_am654_calculate_itap()
>> - Optimize sdhci_am654_calculate_itap()
>> ---
>>   drivers/mmc/host/sdhci_am654.c | 111 +++++++++++++++++++++++++++------
>>   1 file changed, 91 insertions(+), 20 deletions(-)
>>
>> diff --git a/drivers/mmc/host/sdhci_am654.c b/drivers/mmc/host/sdhci_am654.c
>> index d659c59422e1..2c66a965c225 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 +418,100 @@ 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
> 
> Presumably ITAPDLY_LAST_INDEX == ITAPDLY_LENGTH - 1, so perhaps:
> 
> #define ITAPDLY_LAST_INDEX (ITAPDLY_LENGTH - 1)
> 
> Blank line here perhaps.

This does seem easier to read, will add for v3.

> 
>> +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 = {0, 0, 0};
>> +	u8 first_fail_start = 0, last_fail_end = 0;
>> +	int prev_fail_end = -1;
>> +	u8 itap = 0, start_fail = 0, end_fail = 0, pass_length = 0;
>> +	u8 i;
> 
> Some prefer ordering of variable declarations at the beginning of a
> function to be "reverse fir tree" order, in other words, longer lines
> first, e.g.
> 
> 	u8 itap = 0, start_fail = 0, end_fail = 0, pass_length = 0;
> 	u8 first_fail_start = 0, last_fail_end = 0;
> 	struct device *dev = mmc_dev(host->mmc);
> 	struct window pass_window = {0, 0, 0};
> 	int prev_fail_end = -1;
> 	u8 i;

Understood, will add for v3.


> 
>> +
>> +	if (!num_fails)
>> +		return ITAPDLY_LAST_INDEX >> 1;
>> +
>> +	if (fail_window->length == ITAPDLY_LENGTH) {
>> +		dev_err(dev, "No passing ITAPDLY, return 0\n");
>> +		return 0;
>> +	}
>> +
>> +	first_fail_start = fail_window->start;
>> +	last_fail_end = fail_window[num_fails - 1].end;
>> +
>> +	for (i = 0; i < num_fails; i++) {
>> +		start_fail = fail_window[i].start;
>> +		end_fail = fail_window[i].end;
>> +		pass_length = start_fail - (prev_fail_end + 1);
>> +
>> +		if (pass_length > pass_window.length) {
>> +			pass_window.start = prev_fail_end + 1;
>> +			pass_window.length = pass_length;
>> +		}
>> +		prev_fail_end = end_fail;
>> +	}
>> +
>> +	if (!circular_buffer)
>> +		pass_length = ITAPDLY_LAST_INDEX - last_fail_end;
>> +	else
>> +		pass_length = ITAPDLY_LAST_INDEX - last_fail_end + 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;
>> +
>> +	return (itap < 0 || itap > ITAPDLY_LAST_INDEX ? 0 : itap);
> 
> Parentheses are not needed where they are but putting
> them around the condition would make it more readable e.g.
> 
> 	return (itap < 0 || itap > ITAPDLY_LAST_INDEX) ? 0 : itap;
> 
> However (itap < 0) is not possible because itap is an unsigned type
> and if (itap > ITAPDLY_LAST_INDEX) then maybe it would be better
> to return ITAPDLY_LAST_INDEX

You are right about itap < 0, thanks will fix.

About itap > ITAPDLY_LAST_INDEX, this is an error. Why
return ITAPDLY_LAST_INDEX instead of 0?


> 
>> +}
>> +
>>   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;
> 
> Perhaps reverse fir tree

Will add fix here as well.

> 
>> +
>> +	memset(fail_window, 0, sizeof(fail_window[0]) * ITAPDLY_LENGTH);
> 
> This can be:
> 
> 	memset(fail_window, 0, sizeof(fail_window));

This does look simpler, will add for v3.

> 
>>   
>>   	/* 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));
> 
> Parentheses around sdhci_am654->dll_enable are not needed.

Agree, I can remove for v3.

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


My apologies for the late reply and thanks for reviewing.

~ Judith

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