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From: Raul Rangel <rrangel@chromium.org>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: linux-mmc@vger.kernel.org, ernest.zhang@bayhubtech.com,
	djkurtz@chromium.org, linux-kernel@vger.kernel.org,
	Ulf Hansson <ulf.hansson@linaro.org>
Subject: Re: [PATCH 2/3] mmc: sdhci: sdhci-pci-o2micro: Check if controller supports 8-bit width
Date: Wed, 12 Jun 2019 09:08:32 -0600	[thread overview]
Message-ID: <20190612150832.GB27989@google.com> (raw)
In-Reply-To: <d4939761-317c-ee78-b1e5-c2cdd86a12b4@intel.com>

On Wed, Jun 12, 2019 at 04:09:47PM +0300, Adrian Hunter wrote:
> On 10/06/19 9:53 PM, Raul E Rangel wrote:
> > The O2 controller supports 8-bit EMMC access. mmc_select_bus_width()
> > will be used to determine if the MMC supports 8-bit or 4-bit access.
> 
> The problem is that the bit indicates a host controller capability, not how
> many data lines there actually are on the board.  Will this break something
> that does not have 8 lines?

So I asked the controller vendor about that:
> The capability shows the host controller can support 1,4,and 8 bit bus
> data transfer but it also depends on if HW can support it. Driver or FW
> should implement the bus testing procedure that is defined in A.6.3.a
> in JESD84-B51 spec to decide the real bus width that is supported in HW.

This seems to be what `mmc_select_bus_width()` is doing.

I don't actually have any 4-bit hardware to test with though.

Thanks for the review!

  reply	other threads:[~2019-06-12 15:08 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-10 18:53 [PATCH 1/3] mmc: sdhci: sdhci-pci-o2micro: Correctly set bus width when tuning Raul E Rangel
2019-06-10 18:53 ` [PATCH 2/3] mmc: sdhci: sdhci-pci-o2micro: Check if controller supports 8-bit width Raul E Rangel
2019-06-12 13:09   ` Adrian Hunter
2019-06-12 15:08     ` Raul Rangel [this message]
2019-06-13  8:40       ` Adrian Hunter
2019-06-10 18:53 ` [PATCH 3/3] mmc: sdhci: Fix indenting on SDHCI_CTRL_8BITBUS Raul E Rangel
2019-06-12 13:12   ` Adrian Hunter
2019-06-12 13:42   ` Ulf Hansson
2019-06-12 12:53 ` [PATCH 1/3] mmc: sdhci: sdhci-pci-o2micro: Correctly set bus width when tuning Adrian Hunter
2019-06-12 13:36 ` Ulf Hansson
2019-06-12 15:01   ` Raul Rangel
2019-06-17 10:26     ` Ulf Hansson

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