From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gerlando Falauto Subject: i2c: Multiplexed I2C bus core support Date: Wed, 13 Feb 2013 16:36:24 +0100 Message-ID: <511BB2F8.9020300@keymile.com> References: <4C36E6E2.1070307@gmx.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4C36E6E2.1070307-Mmb7MZpHnFY@public.gmane.org> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Rodolfo Giometti , linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Michael Lawnick , Jean Delvare List-Id: linux-i2c@vger.kernel.org Hi everyone, On 07/09/2010 11:07 AM, Michael Lawnick wrote: > Add multiplexed bus core support. I2C multiplexer and switches > like pca954x get instantiated as new adapters per port. > > Signed-off-by: Michael Lawnick > Cc: Jean Delvare I noticed that when you have multiple muxes connected to the same branch, implementation hides some information about the complete i2c topology. So for instance if I have something like (notice there are three PCA9544's "in parallel", each with its own address, which I assume is a bit unusual): # CPU (i2c-0) # '--I2C Mux0 (PCA9547) @ 0x70 # +--Port0 (i2c-1) # +--Port1 (i2c-2) # +--Port2 (i2c-3) # +--Port3 (i2c-4) # +--Port4 (i2c-5) # | '--- I2C Mux1 (PCA9544) @ 0x74 # | | +--Port0 (i2c-9) # | | +--Port1 (i2c-10) # | | +--Port2 (i2c-11) # | | '--Port3 (i2c-12) # | +--- I2C Mux2 (PCA9544) @ 0x71 # | | +--Port0 (i2c-13) # | | +--Port1 (i2c-14) # | | +--Port2 (i2c-15) # | | '--Port3 (i2c-16) # | '--- I2C Mux3 (PCA9544) @ 0x72 # | +--Port0 (i2c-17) # | +--Port1 (i2c-18) # | +--Port2 (i2c-19) # | '--Port3 (i2c-20) # +--Port5 (i2c-6) # +--Port6 (i2c-7) # '--Port7 (i2c-8) under /sys/bus/i2c/devices/ I get: 0-0010 -> ../../../devices/platform/i2c-gpio/i2c-0/0-0010 0-0011 -> ../../../devices/platform/i2c-gpio/i2c-0/0-0011 0-0070 -> ../../../devices/platform/i2c-gpio/i2c-0/0-0070 5-0071 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/5-0071 5-0072 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/5-0072 5-0074 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/5-0074 |2c-0 -> ../../../devices/platform/i2c-gpio/i2c-0 i2c-1 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-1 i2c-2 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-2 i2c-3 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-3 i2c-4 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-4 i2c-5 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5 i2c-6 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-6 i2c-7 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-7 i2c-8 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-8 i2c-9 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/i2c-9 i2c-10 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/i2c-10 i2c-11 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/i2c-11 i2c-12 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/i2c-12 i2c-13 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/i2c-13 i2c-14 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/i2c-14 i2c-15 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/i2c-15 i2c-16 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/i2c-16 i2c-17 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/i2c-17 i2c-18 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/i2c-18 i2c-19 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/i2c-19 i2c-20 -> ../../../devices/platform/i2c-gpio/i2c-0/i2c-5/i2c-20 So I have no way of telling that: i2c-{9,10,11,12} are connected to mux1 at address 0x74 of i2c-5 i2c-{13,14,15,16} are connected to mux2 at address 0x71 of i2c-5 i2c-{17,18,19,20} are connected to mux3 at address 0x72 of i2c-5 because I get: # cat /sys/bus/i2c/devices/i2c-9/name i2c-5-mux (chan_id 0) # cat /sys/bus/i2c/devices/i2c-13/name i2c-5-mux (chan_id 0) which only reveals i2c-9 is the bus segment connected to channel 0 of a mux behind i2c-5, but since there's two of them, I have no way to tell which one... So I guess the easiest thing to do would be to add this information within the .name attribute, though I fear this may somehow turn out not as trivial at it looks. What I'd like most though would be to get some hierarchy as follows: devices/platform/i2c-gpio/i2c-0/0-0070/i2c-5/5-0071/i2c-9 devices/platform/i2c-gpio/i2c-0/0-0070/i2c-5/5-0071/i2c-10 devices/platform/i2c-gpio/i2c-0/0-0070/i2c-5/5-0071/i2c-11 devices/platform/i2c-gpio/i2c-0/0-0070/i2c-5/5-0071/i2c-12 or even something like: devices/platform/i2c-gpio/i2c-0/0-0070/chan-4(=>...i2c-5)/5-0071/chan-0(=>...i2c-9) devices/platform/i2c-gpio/i2c-0/0-0070/chan-4(=>...i2c-5)/5-0071/chan-1(=>...i2c-10) devices/platform/i2c-gpio/i2c-0/0-0070/chan-4(=>...i2c-5)/5-0071/chan-2(=>...i2c-11) devices/platform/i2c-gpio/i2c-0/0-0070/chan-4(=>...i2c-5)/5-0071/chan-3(=>...i2c-12) Would the above seem reasonable? Thanks! Gerlando