linux-kernel - Re: [PATCH 2/2] dt-bindings: rockchip-dw-mshc: add rockchip,default-drv-phase

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Date:	Tue, 10 May 2016 20:50:12 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Shawn Lin <shawn.lin@...k-chips.com>
Cc:	Jaehoon Chung <jh80.chung@...sung.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Brian Norris <briannorris@...omium.org>,
	Heiko Stuebner <heiko@...ech.de>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 2/2] dt-bindings: rockchip-dw-mshc: add rockchip,default-drv-phase

Hi,

On Tue, May 10, 2016 at 7:50 PM, Shawn Lin <shawn.lin@...k-chips.com> wrote:
>>> maybe. But I think 180(downside) is the better.
>
>
> NAK my previous comments here. Downside is better for SRD, but won't
> work for DDR mode. When running in DDR mode, we should use 90 instead.
>
> So let me elaborate a bit more here.
> For DDR mode, one single clk cycle should sending two data bits outside
> to the devices. We need a hold time for both. If 180 is used, the first
> bit occurs around the downside area, which won't be sampled by devices
> on the upside.  So on the upside, the devices will see a zero bit if you
> actually send a one-bit, which makes the devices  generate CRC finally.
>
>
> For this above, 180 for all SDR mode is ok, but 90 should be deployed
> for DDR mode. So simply checking the timing to hardcode it should be
> fine.

OK, I sent out a patch for 180 always.  I can send v2 to use 90 for
DDR modes tomorrow.  ...or feel free to post that yourself if you
want.

We want 90 for all DDR modes?  So MMC_TIMING_UHS_DDR50,
MMC_TIMING_MMC_DDR52, MMC_TIMING_MMC_HS400? (not that we support HS400
in dw_mmc on Rockchip).

-Doug