linux-kernel - Re: [PATCH v2 1/7] mmc: sdhci_am654: Add tuning algorithm for delay chain

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Message-ID: <4618f19d-0b7d-4844-83f7-ff2f4be083d9@intel.com>
Date: Wed, 28 Feb 2024 15:21:46 +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 20/02/24 22:10, Judith Mendez wrote:
> On 2/16/24 11:09 AM, Adrian Hunter wrote:
>> On 7/02/24 03:15, Judith Mendez wrote:
>>> +
>>> +    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?

It doesn't matter.  Just if a value has a better chance to work
if the calculation fails, like maybe ITAPDLY_LAST_INDEX / 2, but
presumably it should not fail.