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Message-ID: <461a19cd-36ce-4c34-890e-655a05a81c58@intel.com>
Date: Fri, 16 Feb 2024 19:09:22 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Judith Mendez <jm@...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
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.
> +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;
> +
> + 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
> +}
> +
> 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
> +
> + memset(fail_window, 0, sizeof(fail_window[0]) * ITAPDLY_LENGTH);
This can be:
memset(fail_window, 0, sizeof(fail_window));
>
> /* 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.
> +
> sdhci_am654_write_itapdly(sdhci_am654, itap);
>
> return 0;
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