Re: [PATCH 2/3] mmc: sdhci: sdhci-pci-o2micro: Check if controller supports 8-bit width

From: Adrian Hunter
Date: Thu Jun 13 2019 - 12:20:50 EST

On 12/06/19 6:08 PM, Raul Rangel wrote:
> 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.

Good point. Can you add this information to the commit message and add a
comment in the code.

> I don't actually have any 4-bit hardware to test with though.
> Thanks for the review!