From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Ball Subject: Re: [PATCH 2/3] powerpc/esdhc: add property to disable the CMD23 Date: Tue, 11 Sep 2012 10:44:32 -0400 Message-ID: <87k3w0y5yn.fsf@octavius.laptop.org> References: <1347347565-17474-1-git-send-email-Chang-Ming.Huang@freescale.com> <1347347565-17474-2-git-send-email-Chang-Ming.Huang@freescale.com> <20120911075429.GA27028@lizard> <20120911080457.GA28235@lizard> <110EED8CC96DFC488B7E717A2027A27C176170@039-SN1MPN1-002.039d.mgd.msft.net> <6D8C87BA-CA06-4215-94F5-63EBF5162B0A@kernel.crashing.org> <2A6FCAE3-288F-4972-90C0-15105932F13E@kernel.crashing.org> Mime-Version: 1.0 Content-Type: text/plain Return-path: Received: from void.printf.net ([89.145.121.20]:46779 "EHLO void.printf.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758618Ab2IKOom (ORCPT ); Tue, 11 Sep 2012 10:44:42 -0400 In-Reply-To: <2A6FCAE3-288F-4972-90C0-15105932F13E@kernel.crashing.org> (Kumar Gala's message of "Tue, 11 Sep 2012 07:49:04 -0500") Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: Kumar Gala Cc: Huang Changming-R66093 , "linuxppc-dev@lists.ozlabs.org list" , linux-mmc@vger.kernel.org, Anton Vorontsov Hi, On Tue, Sep 11 2012, Kumar Gala wrote: > In sdhci_add_host() > > We have the following > > ... > mmc->caps |= MMC_CAP_SDIO_IRQ | MMC_CAP_ERASE | MMC_CAP_CMD23; > > if (host->quirks & SDHCI_QUIRK_MULTIBLOCK_READ_ACMD12) > host->flags |= SDHCI_AUTO_CMD12; > > /* Auto-CMD23 stuff only works in ADMA or PIO. */ > if ((host->version >= SDHCI_SPEC_300) && > ((host->flags & SDHCI_USE_ADMA) || > !(host->flags & SDHCI_USE_SDMA))) { > host->flags |= SDHCI_AUTO_CMD23; > DBG("%s: Auto-CMD23 available\n", mmc_hostname(mmc)); > } else { > DBG("%s: Auto-CMD23 unavailable\n", mmc_hostname(mmc)); > } > > ... > > I'm not clear what the difference is between mmc->caps & host->flags, but shouldn't we move setting MMC_CAP_CMD23 inside the 'Auto-CMD23' if check? The main answer is: No, because CMD23 is distinct from Auto-CMD23. Multiblock transfers (CMD23) date back from MMC cards (which is why they're an MMC host capability) and can also be used in SDHCI. Auto-CMD23 is a new feature in SDHCI 3.0 that reduces the overhead of sending CMD23. It doesn't work if we're using SDMA, though. As for capability vs. flags, the capability is more of an inherent property of the controller, and flags are runtime decisions on whether to use that capability, based on e.g. the presence of a quirk. So, I think the code's correct as written. Feel free to ask more questions if you're investigating a specific problem that you haven't mentioned yet. Thanks, - Chris. -- Chris Ball One Laptop Per Child