From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nikolay Dimitrov Date: Mon, 04 May 2015 16:49:07 +0300 Subject: [U-Boot] [PATCH 1/2] mx6cuboxi: Fix Ethernet PHY detection problem In-Reply-To: <5547677C.4020604@solid-run.com> References: <1430710213-28008-1-git-send-email-festevam@gmail.com> <5546F32B.4020600@mail.bg> <5547677C.4020604@solid-run.com> Message-ID: <554778D3.9040304@mail.bg> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Hi Rabeeh, On 05/04/2015 03:35 PM, Rabeeh Khoury wrote: > On 05/04/2015 07:18 AM, Nikolay Dimitrov wrote: >> Hi Fabio, >> >> On 05/04/2015 06:30 AM, Fabio Estevam wrote: >>> From: Fabio Estevam >>> >>> mx6cuboxi sometimes fails to recognize the Ethernet PHY: >>> >>> Net: Phy 0 not found >>> >>> The explanation comes from a patch from Rabeeh: >>> >>> "The LED_ACT pin on the carrier-one boards had a pull down that >>> forces the phy address to 0x0; where on CuBox-i and the >>> production HummingBoard that pin is connected directly to LED >>> that depending on the pull down strength of the LED it might be >>> sampled as '0' or '1' thus the phy address might appear as either >>> address 0x0 or 0x4." >> >> There's no such thing as "LED pull-down". The forward voltage drop >> of a LED is between 1.65V (red low-power LEDs) to 2.1V (green LEDs) >> to even more for blue LEDs. Even the lowest Vf doesn't qualify as >> logic "0" for LVCMOS33, which is around 1V max (Vil). The LED just >> can't pull-down the voltage level low enough. > This is AR8035 implementation; in reset stage the LED pin is > configured as input, and pull up/down does matter. In this case it > configures the PHY address. > > After reset is deasserted the same LED pin becomes output and then > according to the previous pull/up it should be active high/low (i.e. > driver or sink). I know this. This is why I said that the pin is floating and the R+LED can't define a proper logic level during configuration bootstrapping. In such situations there should be an external pull-up/pull-down to make sure things work properly. Regards, Nikolay