From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from top.free-electrons.com ([176.31.233.9] helo=mail.free-electrons.com) by merlin.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1Vkviu-0005ko-OT for linux-mtd@lists.infradead.org; Mon, 25 Nov 2013 12:57:10 +0000 Date: Mon, 25 Nov 2013 09:56:48 -0300 From: Ezequiel Garcia To: Pekon Gupta Subject: Re: [PATCH] mtd: nand: auto-detection of NAND bus-width from ONFI param or nand_id[] Message-ID: <20131125125647.GF2408@localhost> References: <1385382728-7913-1-git-send-email-pekon@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1385382728-7913-1-git-send-email-pekon@ti.com> Cc: Brian Norris , linux-mtd@lists.infradead.org, balbi@ti.com, Artem Bityutskiy List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Pekon, Thanks for taking care of this! :-) On Mon, Nov 25, 2013 at 06:02:08PM +0530, Pekon Gupta wrote: > This patch is alternative implementation for following commit which introduced > NAND_BUSWIDTH_AUTO for detection of bus-width during device probe > commit 64b37b2a63eb2f80b65c7185f0013f8ffc637ae3 > Author: Matthieu CASTET > AuthorDate: 2012-11-06 > > As NAND device is identified only during nand_scan_ident(), so this patch > assumes that NAND driver may un-initialized or partially congigured while > calling nand_scan_ident(). Hence, this patch does following: > > (1) Temporarily configures 'bus-width=x8' mode before reading ONFI parameters, > (as required by ONFI spec Refer[*]), and then reverts to original bus-width. > This allows nand_flash_detect_onfi() to read ONFI paramers page even if > bus-width was un-initialized or incorrectly configured. > > (2) reconfigures driver with correct bus-width determined by: > - either by reading ONFI param OR > - as found in nand_flash_id[] table > So, any driver-specific callback overrides should be done post nand_scan_ident. > > This patch removes any dependency on either 'DT binding' or 'platform data' to > for determining NAND device bus-width. > > [*] Reference: ONFI spec version 3.1 (section 3.5.3. Target Initialization) > "The Read ID and Read Parameter Page commands only use the lower 8-bits > of the data bus. The host shall not issue commands that use a word > data width on x16 devices until the host determines the device supports > a 16-bit data bus width in the parameter page." > > > Signed-off-by: Pekon Gupta > --- > drivers/mtd/nand/nand_base.c | 43 ++++++++++++++++++------------------------- > include/linux/mtd/nand.h | 7 ------- > 2 files changed, 18 insertions(+), 32 deletions(-) > [..] > + > + /* re-configure driver is bus-width was incorrectly configured */ > + if (busw != (chip->options & NAND_BUSWIDTH_16)) { > + pr_warn("reconfiguring NAND bus width to %d instead %d bit\n", > + busw ? 16 : 8, > + (chip->options & NAND_BUSWIDTH_16) ? 16 : 8); > + chip->options = (chip->options & ~NAND_BUSWIDTH_16) | busw; Looking at this makes me wonder why are we *re* configuring, instead of just configuring. I mean, why do we keep the NAND_BUSWIDTH_16 setting? What use case might need the user to set it, before hand? -- Ezequiel García, Free Electrons Embedded Linux, Kernel and Android Engineering http://free-electrons.com