The 05/13/2021 08:42, Andrew Jeffery wrote:
>
>
> On Mon, 10 May 2021, at 15:33, Steven Lee wrote:
> > The 05/07/2021 15:36, Andrew Jeffery wrote:
> > >
> > >
> > > On Fri, 7 May 2021, at 15:54, Steven Lee wrote:
> > > > The 05/07/2021 09:32, Andrew Jeffery wrote:
> > > > >
> > > > >
> > > > > On Thu, 6 May 2021, at 19:54, Philipp Zabel wrote:
> > > > > > Hi Steven,
> > > > > >
> > > > > > On Thu, May 06, 2021 at 06:03:12PM +0800, Steven Lee wrote:
> > > > > > > + if (info) {
> > > > > > > + if (info->flag & PROBE_AFTER_ASSET_DEASSERT) {
> > > > > > > + sdc->rst = devm_reset_control_get(&pdev->dev, NULL);
> > > > > >
> > > > > > Please use devm_reset_control_get_exclusive() or
> > > > > > devm_reset_control_get_optional_exclusive().
> > > > > >
> > > > > > > + if (!IS_ERR(sdc->rst)) {
> > > > > >
> > > > > > Please just return errors here instead of ignoring them.
> > > > > > The reset_control_get_optional variants return NULL in case the
> > > > > > device node doesn't contain a resets phandle, in case you really
> > > > > > consider this reset to be optional even though the flag is set?
> > > > >
> > > > > It feels like we should get rid of the flag and leave it to the
> > > > > devicetree.
> > > > >
> > > >
> > > > Do you mean adding a flag, for instance, "mmc-reset" in the
> > > > device tree and call of_property_read_bool() in aspeed_sdc_probe()?
> > > >
> > > > > I'm still kind of surprised it's not something we want to do for the
> > > > > 2400 and 2500 as well.
> > > > >
> > > >
> > > > Per discussion with the chip designer, AST2400 and AST2500 doesn't need
> > > > this implementation since the chip design is different to AST2600.
> > >
> > > So digging a bit more deeply on this, it looks like the reset is
> > > already taken care of by drivers/clk/clk-ast2600.c in the
> > > clk_prepare_enable() path.
> > >
> > > clk-ast2600 handles resets when enabling the clock for most peripherals:
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/clk/clk-ast2600.c?h=v5.12#n276
> > >
> > > and this is true for both the SD controller and the eMMC controller:
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/clk/clk-ast2600.c?h=v5.12#n94
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/clk/clk-ast2600.c?h=v5.12#n88
> > >
> > > If this weren't the case you'd specify a reset property in the SD/eMMC
> > > devicetree nodes for the 2600 and then use
> > > devm_reset_control_get_optional_exclusive() as Philipp suggested. See
> > > the reset binding here:
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/reset/reset.txt?h=v5.12
> > >
> > > So on the surface it seems the reset handling in this patch is
> > > unnecessary. Have you observed an issue with the SoC that means it's
> > > required?
> > >
> >
> > Yes, you are right, aspeed_sdc_probe() calls clk_prepare_enable(),
> > aspeed_g6_clk_enable() does reset eMMC.
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/mmc/host/sdhci-of-aspeed.c#n496
> >
> > However, the clock of eMMC is enabled in my u-boot(2019.04).
> > So it is retruned in the condition of aspeed_g6_clk_is_enabled() below
> > and doesn't reset eMMC.
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/clk/clk-ast2600.c?h=v5.12#n285
>
> Okay, so what's the issue that the patch addresses? Is there a bug?
> Presumably if u-boot isn't making use of the eMMC the clock won't be
> on, so we'll do the reset if the kernel wants to make use of the
> device. If u-boot _is_ using the eMMC, u-boot will have done the
> correct clock enable/reset sequence and so the controller should be
> ready to go?
>
> The only potential issue remaining is u-boot leaving the controller in
> a configuration the kernel isn't expecting when handing over. If that's
> the issue then we've forgotten to do some specific initialisation (i.e.
> not just reset the entire thing) of the controller in the driver probe
> path, right?
>
If DMA engine is used before probing eMMC in kernel stage,
eMMC controller may have unexpected behavior when re-exectuing
identifying process.
Thus, we need to reset at the beginning of kernel since
kernel is a new stage. We should not assume some one do something
before.
> FWIW I haven't recently seen any poor behaviour from the controller or
> driver. For us (IBM) it seems to be working well since we sorted out
> the phase configuration.
>
Yes, you are right, everything work well currently. But, kernel is a new
stage, we cannot assume eMMC controller is at initial state when
entering kernel stage.
> Andrew
