From: Dmitry Torokhov <email@example.com> To: Furquan Shaikh <firstname.lastname@example.org> Cc: Dan Carpenter <email@example.com>, firstname.lastname@example.org, Linux Kernel Mailing List <email@example.com> Subject: Re: [PATCH] input: raydium_ts_i2c: Do not split tx transactions Date: Mon, 30 Nov 2020 23:06:15 -0800 [thread overview] Message-ID: <20201201070615.GT2034289@dtor-ws> (raw) In-Reply-To: <CAEGmHFGYuM91U+Tvq+YDt180cfHQKnOKMY5ToHZ7v44fOsfirstname.lastname@example.org> On Mon, Nov 30, 2020 at 10:54:46PM -0800, Furquan Shaikh wrote: > Hello Dmitry, > > On Mon, Nov 30, 2020 at 10:28 PM Dmitry Torokhov > <email@example.com> wrote: > > > > Hi Furquan, > > > > On Mon, Nov 30, 2020 at 10:00:50PM -0800, Furquan Shaikh wrote: > > > Raydium device does not like splitting of tx transactions into > > > multiple messages - one for the register address and one for the > > > actual data. This results in incorrect behavior on the device side. > > > > > > This change updates raydium_i2c_read and raydium_i2c_write to create > > > i2c_msg arrays separately and passes those arrays into > > > raydium_i2c_xfer which decides based on the address whether the bank > > > switch command should be sent. The bank switch header is still added > > > by raydium_i2c_read and raydium_i2c_write to ensure that all these > > > operations are performed as part of a single I2C transfer. It > > > guarantees that no other transactions are initiated to any other > > > device on the same bus after the bank switch command is sent. > > > > i2c_transfer locks the bus [segment] for the entire time, so this > > explanation on why the change is needed does not make sense. > > The actual problem is with raydium_i2c_write chopping off the write > data into 2 messages -- one for register address and other for actual > data. Raydium devices do not like that. Hence, this change to ensure > that the register address and actual data are packaged into a single > message. The latter part of the above comment attempts to explain why > the bank switch message is added to xfer array in raydium_i2c_read > and raydium_i2c_write instead of sending a separate message in > raydium_i2c_xfer i.e. to ensure that the read/write xfer and bank > switch are sent to i2c_transfer as a single array of messages so that > they can be handled as an atomic operation from the perspective of > communication with this device on the bus. OK, I see. > > > > > Also, does it help if you mark the data message as I2C_M_NOSTART in case > > of writes? > > That is a great suggestion. I think this would be helpful in this > scenario. Let me follow-up on this to see if it helps with the current > problem. > > > > > I also wonder if we should convert the driver to regmap, which should > > help with handling the bank switch as well as figuring out if it can do > > "gather write" or fall back to allocating an additional send buffer. > > I will start with the above suggestion and fallback to this if that > doesn't work. So my understanding is that not all I2C adapters support I2C_M_NOSTART so that is why regmap is nice as it hides it all away and figures things on its own. So simple solution of I2C_M_NOSTART might be a quick fix for Chrome OS kernel, but we'd either need to always use more expensive 2nd buffer as is in your patch, or regmap. Thanks. -- Dmitry
next prev parent reply other threads:[~2020-12-01 7:06 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-12-01 6:00 Furquan Shaikh 2020-12-01 6:28 ` Dmitry Torokhov 2020-12-01 6:54 ` Furquan Shaikh 2020-12-01 7:06 ` Dmitry Torokhov [this message] 2020-12-01 7:15 ` Furquan Shaikh 2020-12-05 0:59 ` [PATCH v2] " Furquan Shaikh 2020-12-07 6:20 ` Dmitry Torokhov
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