Re: [PATCH v3 5/5] mmc: sdhci-of-aspeed: Assert/Deassert reset signal before probing eMMC

[Steven Lee <steven_lee@aspeedtech.com>]

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


> Andrew