Re: [PATCH] sdhci: adjust sd 3.0 host controller spec clock divider

Hein_Tibosch
2010-10-05T17:56:06Z

Hi Philip, Chris,

On 5-10-2010 10:34, Chris Ball wrote:
> Hi David,
>
> On Thu, Sep 30, 2010 at 08:03:14PM -0700, Philip Rakity wrote:
>> From: Philip Rakity <prakity@marvell.com>
>> Date: Thu, 30 Sep 2010 15:34:24 -0700
>> Subject: [PATCH] sdhci: adjust sd 3.0 host controller spec clock divider
>>
>> The sd 3.0 host spec does not require the clock divider to be a power of 2.

The text and code for sd 3.0 was talking about a multiple of 2, not a power of 2

>> Signed-off-by: Philip Rakity <prakity@marvell.com>
>> ---
>> drivers/mmc/host/sdhci.c | 8 +++-----
>> 1 files changed, 3 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>> index 96c7f60..73a94fe 100644
>> --- a/drivers/mmc/host/sdhci.c
>> +++ b/drivers/mmc/host/sdhci.c
>> @@ -1003,14 +1003,12 @@ static void sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
>> goto out;
>>
>> if (host->version >= SDHCI_SPEC_300) {
>> - /* Version 3.00 divisors must be a multiple of 2. */
>> if (host->max_clk <= clock)
>> div = 1;
>> else {
>> - for (div = 2; div < SDHCI_MAX_DIV_SPEC_300; div += 2) {
>> - if ((host->max_clk / div) <= clock)
>> - break;
>> - }
>> + div = host->max_clk/clock;
>> + if (host->max_clk % clock)
>> + div++;
If you mean to divide and round up, wouldn't :

+ div = DIV_ROUND_UP (host->max_clk, clock);

be nicer and cheaper?

Can SDHCI_MAX_DIV_SPEC_300 be dropped safely?

(don't have access to the sd 3.0 specs neither)

Hein