Re: [PATCH 3/4 v5] SDHCI: add sdhci_get_cd callback to detect the card

[Jaehoon Chung <jh80.chung@samsung.com>]

On 12/16/2011 12:25 PM, Huang Changming-R66093 wrote:

>>> I am very confused, why do we read the present state register on every
>> request?
>>
>> How long time read the present state register?
> Even if one line code is performed, I think it need time to complete.
> 
>>> My codes are added to the function mmc_sd_detect in file core/sd.c
>>> Function mmc_rescan has detect the card present state repeatedly, so I
>> think we don't need to detect the card state on every request.
>>> So I think the codes to detect the card present state in sdhci_request
>> should be removed to improve the performance.
>>
>> How did you get the performance benefit?
> Do you know there are many tools to run the performance?
> IPForward/IPSEC for network, iozone for SATA/SDHC...
> 
> We have the performance result from our platform, the result will decrease 2%~5%!
> 
> If the driver has the option 'MMC_CAP_NEEDS_POLL' (many driver enable this option) and the card is always present, the driver will send the command "mmc_send_status" to ask the card state repeatedly.
> Do you know what it means? Many interrupts will be generated even if the system is reading from/writing to the SD/MMC card.
> 
>> And mmc_rescan is repeatedly for SD-card?
>> If mmc_rescan is repeatedly, that reason is the below code. (just my
>> thinking)
>>
>> if (host->caps & MMC_CAP_NEEDS_POLL)
>> 	mmc_schedule_delayed_work(&host->detect, HZ);
>>
>> what is your point related with mmc_rescan?
>> I didn't understand yours..
> 
> There are some controllers don't support the card detect, the SDHCI_CARD_PRESENT is forever one. And some controller must enable the MMC_CAP_NEEDS_POLL option (about this, you can search the folder mmc/host/), that means mmc_rescan will be run repeatedly.
> In these cases, if we detect the card state though command mmc_send_status, a lot of interrupts will be generated.

I know that...Some controller didn't support the card detect...But I think you can control this problem with SDHCI_QUIRK_BROKEN_CARD_DETECTION and some flags.
If controller is always polling for card status, that's inefficient.
I use the SDHCI_QUIRK_BROKEN_CARD_DETECTION, but didn't generate the interrupt at every time(didn't polling)
I think you can solve this problem in sdhci-xxx.c, not in sdhci.c

> 
> For the transaction from/to SD card, we don't need to check the card present state, it should be done in other area.
> So I don't think it is correct to detect card state in function sdhci_request. 

> 

> 
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