From mboxrd@z Thu Jan 1 00:00:00 1970 From: LW@KARO-electronics.de (Lothar =?UTF-8?B?V2HDn21hbm4=?=) Date: Thu, 7 Aug 2014 15:18:42 +0200 Subject: [PATCH v6 1/2] i2c: imx: add DMA support for freescale i2c driver In-Reply-To: <6537011f698c4c7faaf5b66b870afbd2@BLUPR03MB373.namprd03.prod.outlook.com> References: <1407232563-10856-1-git-send-email-yao.yuan@freescale.com> <1407232563-10856-2-git-send-email-yao.yuan@freescale.com> <41705e1e4c604240ba96333a03d5c544@BLUPR03MB373.namprd03.prod.outlook.com> <14d042bbcfb04308bfb3a1db18e46bec@BL2PR03MB338.namprd03.prod.outlook.com> <31f8f5504fc24d999f5af74338602bed@BLUPR03MB373.namprd03.prod.outlook.com> <6537011f698c4c7faaf5b66b870afbd2@BLUPR03MB373.namprd03.prod.outlook.com> Message-ID: <20140807151842.1dddaf24@ipc1.ka-ro> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi, fugang.duan at freescale.com wrote: > From: Yuan Yao-B46683 Data: Thursday, August 07, 2014 4:05 PM > >To: Duan Fugang-B38611; wsa at the-dreams.de; marex at denx.de > >Cc: LW at KARO-electronics.de; mark.rutland at arm.com; shawn.guo at linaro.org; > >linux-kernel at vger.kernel.org; linux-arm-kernel at lists.infradead.org; linux- > >i2c at vger.kernel.org; Li Frank-B20596 > >Subject: RE: [PATCH v6 1/2] i2c: imx: add DMA support for freescale i2c > >driver > > > >Hi Fugang, > > > >> >> >+ /* Waiting for Transfer complete. */ > >> >> >+ while (timeout--) { > >> >> >+ temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2SR); > >> >> >+ if (temp & I2SR_ICF) > >> >> >+ break; > >> >> >+ udelay(10); > >> >> >+ } > >> >> Whether there have better method like interrupt to avoid dead wait > >> >> here until timeout ? > >> > > >> >Can you give me more suggestion? We have discussed it with our team, > >> >It seems the short query wait is necessary. > >> > > >> At least, you can use schdule_timeout() instead of udelay() ? > > > >In fact, the waiting time normally is less than 10-50us, but the minimum > >time interval for schdule_timeout() is 1 jiffies. > >So maybe schdule_timeout() is not very necessary? > > > Oh, if the waiting time is 10 ~ 50us, you can use usleep_range(10, 50). > The loop is not meant to generate a certain delay, but to wait for some HW flag to change within a certain time frame. So usleep_range() is rather inadequate here! But looking a little closer at the function, the timeout value seems to be rather bogus to me. The loop counter 'timeout' is initialized from the constant IMX_I2C_DMA_TIMEOUT which is also used in |wait_for_completion_interruptible_timeout( | &i2c_imx->dma->cmd_complete, | msecs_to_jiffies(IMX_I2C_DMA_TIMEOUT)); ^^^^^^^^^^^^^^^^^^^ as a number of milliseconds to wait for DMA completion. Lothar Wa?mann -- ___________________________________________________________ Ka-Ro electronics GmbH | Pascalstra?e 22 | D - 52076 Aachen Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10 Gesch?ftsf?hrer: Matthias Kaussen Handelsregistereintrag: Amtsgericht Aachen, HRB 4996 www.karo-electronics.de | info at karo-electronics.de ___________________________________________________________