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. > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-mmc" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
