From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm0-x234.google.com ([2a00:1450:400c:c09::234]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1fGjpk-0006Pc-Ac for linux-mtd@lists.infradead.org; Thu, 10 May 2018 11:34:05 +0000 Received: by mail-wm0-x234.google.com with SMTP id l1-v6so3794300wmb.2 for ; Thu, 10 May 2018 04:33:53 -0700 (PDT) Subject: Re: [PATCH/RFC] mtd: spi-nor: honour max_message_size for spi-nor writes. To: NeilBrown , Boris Brezillon Cc: David Woodhouse , Brian Norris , Richard Weinberger , linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org References: <87efj1kw9u.fsf@notabene.neil.brown.name> <20180509160240.23ef11f2@bbrezillon> <87vabwa2gm.fsf@notabene.neil.brown.name> From: Marek Vasut Message-ID: Date: Thu, 10 May 2018 12:21:52 +0200 MIME-Version: 1.0 In-Reply-To: <87vabwa2gm.fsf@notabene.neil.brown.name> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 05/10/2018 12:28 AM, NeilBrown wrote: > On Wed, May 09 2018, Boris Brezillon wrote: > >> On Fri, 27 Apr 2018 16:18:05 +1000 >> NeilBrown wrote: >> >>> Hi, >>> I've labeled this an RFC because I'm really not sure about removing the >>> error path from spi_nor_write() -- maybe that really matters. But on >>> my hardware, performing multiple small spi writes to the flash seems >>> to work. >>> >>> The spi driver is drivers/staging/mt7621-spi. Possibly this needs to >>> use DMA instead of a FIFO (assuming the hardware can) - or maybe >>> drivers/spi/spi-mt65xx.c can be made to work on this hardware, though >>> that is for an ARM SOC and mt7621 is a MIPS SOC. >>> >>> I note that openwrt has similar patches: >>> target/linux/generic/pending-4.14/450-mtd-spi-nor-allow-NOR-driver-to-write-fewer-bytes-th.patch >>> >>> They also change the spi driver to do a short write, rather >>> than change m25p80 to request a short write. >>> >>> Is there something horribly wrong with this? >> >> Marek, any opinion on this patch? >> > > Hi, > thanks for following up. > I have since found that I don't need this patch, though maybe others > still do(??). > My hardware can only send 36 bytes and receive 32 in a single > transaction. However I can run a sequence of transactions > to process a whole message no matter how large that message is. As > long as I keep chip-select asserted, all the slave device sees is that > the clock period isn't quite constant, and the slave shouldn't care > much about that. > When reading from flash, I found that handling large messages with > multiple hardware transactions was 50% faster than breaking the > read down into lots of 32 byte messages. > > So, I won't object if this patch is forgotten. Thanks for > your time anyway. Nice, which hardware is that ? -- Best regards, Marek Vasut