From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Garry Subject: Re: [PATCH 2/3] spi: Add HiSilicon v3xx SPI NOR flash controller driver Date: Tue, 5 Nov 2019 16:04:09 +0000 Message-ID: References: <1572886297-45400-1-git-send-email-john.garry@huawei.com> <1572886297-45400-3-git-send-email-john.garry@huawei.com> <20191104192406.GH5238@sirena.co.uk> <855a67dc-1356-a763-e374-540f6ac400ab@huawei.com> <20191105110504.GA4500@sirena.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Cc: , , , , , , , To: Mark Brown Return-path: In-Reply-To: <20191105110504.GA4500@sirena.co.uk> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-spi.vger.kernel.org On 05/11/2019 11:05, Mark Brown wrote: > On Tue, Nov 05, 2019 at 10:58:39AM +0000, John Garry wrote: >> On 04/11/2019 19:24, Mark Brown wrote: >>> On Tue, Nov 05, 2019 at 12:51:36AM +0800, John Garry wrote: > >>>> + if (len) { >>>> + u32 val; >>>> + >>>> + val = __raw_readl(host->regbase + CMD_DATABUF(words)); >>>> + >>>> + to += words * 4; >>>> + for (i = 0; i < len; i++, val >>= 8, to++) >>>> + *to = (u8)val; >>>> + } >>>> + } else { >>>> + for (i = 0; i < DIV_ROUND_UP(len, 4); i++) { >>>> + u32 val = __raw_readl(host->regbase + CMD_DATABUF(i)); >>>> + int j; > >>> The more usual pattern for these would be to do some unaligned accesses >>> for the start/end of the buffer to get to alignment and then transfer >>> the rest as aligned data. > >> Yeah, I understand you, but for that I would need to generate multiple >> transactions in the driver, and I wanted to keep 1x transaction per >> spi_controller_mem_ops.exec_op call. > Hi Mark, >> So maybe I can do some trickery in my adjust_op_size method to generate >> these multiple transactions: a. any unaligned start data b. the 32b-aligned >> data b. unaligned end. I think that the HW should be able to handle that. > > Right, that's what I was expecting. > So that should work for xfer data commands, but generally the read/write reg commands in the SPI NOR layer would not use spi_mem_adjust_op_size(), like spi-nor.c:spi_nor_read_id(), as an example. For these, I should be able to guarantee start alignment (since the buffer is kmalloc'ed), but not end alignment, so would still require 4-byte + single byte copies for these. Thanks, John