> -----Original Message----- > From: Adrian Hunter [mailto:adrian.hun...@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-ow...@vger.kernel.org [mailto:linux-mmc- > >> ow...@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, r66...@freescale.com wrote: > >>> From: Jerry Huang <chang-ming.hu...@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. -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
