Re: [PATCH 2/4] MMC/SD: Add callback function to detect card

[Adrian Hunter <adrian.hunter@intel.com>]

On 13/12/11 10:26, Huang Changming-R66093 wrote:
> 
> 
>> -----Original Message-----
>> From: Adrian Hunter [mailto:adrian.hunter@intel.com]
>> Sent: Tuesday, December 13, 2011 4:01 PM
>> To: Huang Changming-R66093
>> Cc: linux-mmc@vger.kernel.org
>> Subject: Re: [PATCH 2/4] MMC/SD: Add callback function to detect card
>>
>> On 13/12/11 09:25, Huang Changming-R66093 wrote:
>>>
>>>
>>>> -----Original Message-----
>>>> From: linux-mmc-owner@vger.kernel.org [mailto:linux-mmc-
>>>> owner@vger.kernel.org] On Behalf Of Adrian Hunter
>>>> Sent: Friday, December 09, 2011 6:03 PM
>>>> To: Huang Changming-R66093
>>>> Cc: linux-mmc@vger.kernel.org; Huang Changming-R66093
>>>> Subject: Re: [PATCH 2/4] MMC/SD: Add callback function to detect card
>>>>
>>>> On 05/12/11 11:23, r66093@freescale.com wrote:
>>>>> From: Jerry Huang <Chang-Ming.Huang@freescale.com>
>>>>>
>>>>> In order to check whether the card has been removed, the function
>>>>> mmc_send_status() will send command CMD13 to card and ask the card
>>>>> to send its status register to sdhc driver, which will generate many
>>>>> interrupts repeatedly and make the system performance bad.
>>>>
>>>> That should not be true.  sdhci.c will not send a command to the card
>>>> if the card is not present i.e. see this excerpt from
>>>> sdhci_request():
>>>>
>>>>
>>>> 	/* If polling, assume that the card is always present. */
>>>> 	if (host->quirks & SDHCI_QUIRK_BROKEN_CARD_DETECTION)
>>>> 		present = true;
>>>> 	else
>>>> 		present = sdhci_readl(host, SDHCI_PRESENT_STATE) &
>>>> 				SDHCI_CARD_PRESENT;
>>>>
>>>> 	if (!present || host->flags & SDHCI_DEVICE_DEAD) {
>>>> 		host->mrq->cmd->error = -ENOMEDIUM;
>>>> 		tasklet_schedule(&host->finish_tasklet);
>>>> --
>>> But, for some controller, this field of SDHCI_PRESENT_STATE register is
>> reserved and always is 1. When the card is absent, many command will try
>> to send to the card, and generate many interrupt.
>>> If even controller can detect the card state, if the card is absent as
>> you said, this command can't send to card. But, when card is present,
>> there will be many command to the card and many interrupts will be
>> generated, that will affect the performance.
>>> So, I don't think this comment is not correct.
>>>
>>>
>>>
>>
>> You patch uses (SDHCI_CARD_PRESENT | SDHCI_CARD_CDPL) Does that mean
>> SDHCI_CARD_CDPL does work in that case?
> No.
> The SDHCI_CARD_CDPL[bit13] reflect the pin level:
> CDPL: Card detect pin level. This bit reflects the inverse value of the SDHC_CD pin for the card socket.
> 0 No card present (SDHC_CD = 1)
> 1 Card present (SDHC_CD = 0)
> 
> So, this bit has the same effect as SDHCI_CARD_PRESENT[bit15], the difference is that debouncing is not performed on this bit.
> 
> Freescale's controller supports the card detection, if card is present, none-zero will be returned, otherwise, zero will be returned.
> 
> You can see my other patch [3/4], I add one callback to detect the card state in special platform: if the controller supports card detection, this callback will be performed in special platform (e.g. sdhci-of-esdhc.c) and return the card state (present or absent), if controller doesn't support card detection, this callback will be not performed and return -ENOSYS.

OK, but the point is, the request can be stopped in sdhci_request().
Can you just add your callback there?

> 
> 
> 
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