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Message-ID: <1bbefc95-a671-492d-8d66-42abecbc4db0@ti.com>
Date: Wed, 31 Jan 2024 14:27:27 -0600
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Subject: Re: [RFC PATCH 01/13] drivers: mmc: host: sdhci_am654: Add tuning
 algorithm for delay chain
Content-Language: en-US
To: Vignesh Raghavendra <vigneshr@ti.com>,
        Ulf Hansson
	<ulf.hansson@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof
 Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley
	<conor+dt@kernel.org>
CC: Adrian Hunter <adrian.hunter@intel.com>, <linux-mmc@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, Nishanth Menon <nm@ti.com>,
        Andrew Davis
	<afd@ti.com>, Udit Kumar <u-kumar1@ti.com>,
        Roger Quadros
	<rogerq@kernel.org>, <devicetree@vger.kernel.org>,
        Randolph Sapp <rs@ti.com>
References: <20240131003714.2779593-1-jm@ti.com>
 <20240131003714.2779593-2-jm@ti.com>
 <d58f1501-ea64-4964-ac32-a3604178dc6f@ti.com>
From: Judith Mendez <jm@ti.com>
In-Reply-To: <d58f1501-ea64-4964-ac32-a3604178dc6f@ti.com>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 7bit

On 1/31/24 5:04 AM, Vignesh Raghavendra wrote:
> Hi Judith,
> 
> On 31/01/24 06:07, 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
>>
>> Signed-off-by: Judith Mendez <jm@ti.com>
>> ---
> 
> 
> $subject prefix should be
> 
>   mmc: sdhci_am654:
> 
> See git log --oneline drivers/mmc/host/sdhci_am654.c for precedence.

Thanks, will add in v1.

> 
>>   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..59d205511312 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 calculate_itap(struct sdhci_host *host, struct window *fail_window,
>> +			  u8 num_fails, bool circular_buffer)
> 
> 
> s/calculate_itap/sdhci_am654_calculate_itap/ to keep function naming
> consistent within the file

Will add.

> 
>> +{
>> +	struct device *dev = mmc_dev(host->mmc);
>> +	struct window pass_window, first_fail, last_fail;
>> +	u8 itap = 0, start_fail = 0, end_fail = 0, pass_length = 0;
>> +	int prev_end_fail = -1;
>> +
>> +	memset(&pass_window, 0, sizeof(pass_window));
>> +	memset(&first_fail, 0, sizeof(first_fail));
>> +	memset(&last_fail, 0, sizeof(last_fail));
>> +
>> +	if (!num_fails) {
>> +		return ITAPDLY_LAST_INDEX >> 1;
>> +	} else if (fail_window->length == ITAPDLY_LENGTH) {
>> +		dev_warn(dev, "No passing ITAPDLY, return 0\n");
> 
> Drop return 0 in dev_warn()

Good idea, will update itap value here then.

> 
>> +		return 0;
> 
> Should this be an error?

It is an error, but I thought it was a good idea to return 0 in case all 
ITAPDLY values fail and report this via dev_warn or dev_error. For now I 
can use dev_error.

> 
>> +	} else {
>> +		for (int i = 0; i < num_fails; i++) {
> 
> 
> please avoid inline declaration to align with rest of the file.

Will do.
> 
>> +			start_fail = fail_window[i].start;
>> +			end_fail = fail_window[i].end;
>> +
>> +			if (i == 0) {
>> +				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, i;
>> +
>> +	for (i = 0; i < ITAPDLY_LENGTH; i++)
>> +		memset(&fail_window[i], 0, sizeof(fail_window[0]));
> 
> Don't need for() loop, just memset entire array at once. Something like:
> 
> memset(fail_window, 0, sizeof(fail_window[0]) * ITAPDLY_LENGTH);

Great, will add this, thanks.

> 
>>   
>>   	/* 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++;
> 
> These is some tab vs space mangling here.

I will fix this. (:

> 
>> +
>> +	itap = calculate_itap(host, &fail_window[0], fail_index,
>> +			      (sdhci_am654->dll_enable ? true : false));
>> +
>>   	sdhci_am654_write_itapdly(sdhci_am654, itap);
>>   
>>   	return 0;
>