[U-Boot] [PATCH v4 2/3] mmc: dw_mmc: Support bypass mode with the get_mmc_clk() method

[Marek Vasut]

On Friday, August 07, 2015 at 05:00:24 AM, Simon Glass wrote:
> Hi Marek,

Hi Simon,

> On 6 August 2015 at 20:58, Marek Vasut <marex at denx.de> wrote:
> > On Friday, August 07, 2015 at 04:54:42 AM, Simon Glass wrote:
> >> Hi Marek,
> > 
> > Hi Simon,
> > 
> >> On 6 August 2015 at 20:51, Marek Vasut <marex at denx.de> wrote:
> >> > On Friday, August 07, 2015 at 04:16:28 AM, Simon Glass wrote:
> >> >> Some SoCs want to adjust the input clock to the DWMMC block as a way
> >> >> of controlling the MMC bus clock. Update the get_mmc_clk() method to
> >> >> support this.
> >> >> 
> >> >> Signed-off-by: Simon Glass <sjg at chromium.org>
> >> > 
> >> > Hi Simon,
> >> > 
> >> >> ---
> >> >> 
> >> >> Changes in v4:
> >> >> - Update commit message to indicate this patch is for the dw_mmc
> >> >> driver
> >> >> 
> >> >>  drivers/mmc/dw_mmc.c        |  2 +-
> >> >>  drivers/mmc/exynos_dw_mmc.c |  2 +-
> >> >>  include/dwmmc.h             | 16 +++++++++++++++-
> >> >>  3 files changed, 17 insertions(+), 3 deletions(-)
> >> >> 
> >> >> diff --git a/drivers/mmc/dw_mmc.c b/drivers/mmc/dw_mmc.c
> >> >> index 8f28d7e..a034c3f 100644
> >> >> --- a/drivers/mmc/dw_mmc.c
> >> >> +++ b/drivers/mmc/dw_mmc.c
> >> >> @@ -248,7 +248,7 @@ static int dwmci_setup_bus(struct dwmci_host
> >> >> *host, u32 freq) * host->bus_hz should be set by user.
> >> >> 
> >> >>        */
> >> >>       
> >> >>       if (host->get_mmc_clk)
> >> >> 
> >> >> -             sclk = host->get_mmc_clk(host);
> >> >> +             sclk = host->get_mmc_clk(host, freq);
> >> > 
> >> > Why are you passing the @freq into get_mmc_clk() ? Shouldn't you call
> >> > some clock framework function to determine the input frequency of the
> >> > DWMMC block from within the get_mmc_clk() implementation instead ?
> >> > What do you think please ?
> >> 
> >> Well, yes. If such a clock frame work existed I would call it :-) We
> >> do have a uclass now so we are getting there.
> > 
> > Excellent, so do you really need this kind of patch ? :) Why don't you
> > make just some kind of function -- get_dwmmc_clock() -- and call it
> > instead ?
> 
> This is sort-of what is happening. It is calling a function in the
> host controller - i.e. the SoC's MMC controller. It is one step closer
> to knowing the input clock to the dwmmc input clock. Note that it is
> not the clock of the MMC bus itself, but the input clock to the dwmmc
> logic block.

I don't think I quite understand what you mean here. We're talking about
obtaining the frequency of the clock which go into the DWMMC IP block,
right ?

So, if you implement a function, say -- dwmmc_get_upstream_clock() -- and
call it from within the implementation of the .get_mmc_clk(), which is
specific for that particular chip of yours*, you don't need this patch.
Or am I really missing something fundamental ?

*the .get_mmc_clk() is specific to a chip, see for example exynos_dw_mmc.c

Best regards,
Marek Vasut