linux-kernel - Re: [PATCH 3/4] powerpc/pseries/iommu: Move window-removing part of remove_ddw into remove_dma

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Message-ID: <ccf7b591f2bf61ba4705699b2e2b050c3cf48d99.camel@gmail.com>
Date:   Mon, 22 Jun 2020 15:59:14 -0300
From:   Leonardo Bras <leobras.c@...il.com>
To:     Alexey Kardashevskiy <aik@...abs.ru>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Ram Pai <linuxram@...ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] powerpc/pseries/iommu: Move window-removing part of
 remove_ddw into remove_dma_window

Hello Alexey, thanks for the feedback!

On Mon, 2020-06-22 at 20:02 +1000, Alexey Kardashevskiy wrote:
> 
> On 19/06/2020 15:06, Leonardo Bras wrote:
> > Move the window-removing part of remove_ddw into a new function
> > (remove_dma_window), so it can be used to remove other DMA windows.
> > 
> > It's useful for removing DMA windows that don't create DIRECT64_PROPNAME
> > property, like the default DMA window from the device, which uses
> > "ibm,dma-window".
> > 
> > Signed-off-by: Leonardo Bras <leobras.c@...il.com>
> > ---
> >  arch/powerpc/platforms/pseries/iommu.c | 53 +++++++++++++++-----------
> >  1 file changed, 31 insertions(+), 22 deletions(-)
> > 
> > diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
> > index 5e1fbc176a37..de633f6ae093 100644
> > --- a/arch/powerpc/platforms/pseries/iommu.c
> > +++ b/arch/powerpc/platforms/pseries/iommu.c
> > @@ -767,25 +767,14 @@ static int __init disable_ddw_setup(char *str)
> >  
> >  early_param("disable_ddw", disable_ddw_setup);
> >  
> > -static void remove_ddw(struct device_node *np, bool remove_prop)
> > +static void remove_dma_window(struct device_node *pdn, u32 *ddw_avail,
> 
> You do not need the entire ddw_avail here, pass just the token you need.

Well, I just emulated the behavior of create_ddw() and query_ddw() as
both just pass the array instead of the token, even though they only
use a single token. 

I think it's to make the rest of the code independent of the design of
the "ibm,ddw-applicable" array, and if it changes, only local changes
on the functions will be needed.

> Also, despite this particular file, the "pdn" name is usually used for
> struct pci_dn (not device_node), let's keep it that way.

Sure, I got confused for some time about this, as we have:
static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn).
but on *_ddw() we have "struct pci_dn *pdn".

I will also add a patch that renames those 'struct device_node *pdn' to
something like 'struct device_node *parent_dn'.

> > +			      struct property *win)
> >  {
> >  	struct dynamic_dma_window_prop *dwp;
> > -	struct property *win64;
> > -	u32 ddw_avail[3];
> >  	u64 liobn;
> > -	int ret = 0;
> > -
> > -	ret = of_property_read_u32_array(np, "ibm,ddw-applicable",
> > -					 &ddw_avail[0], 3);
> > -
> > -	win64 = of_find_property(np, DIRECT64_PROPNAME, NULL);
> > -	if (!win64)
> > -		return;
> > -
> > -	if (ret || win64->length < sizeof(*dwp))
> > -		goto delprop;
> > +	int ret;
> >  
> > -	dwp = win64->value;
> > +	dwp = win->value;
> >  	liobn = (u64)be32_to_cpu(dwp->liobn);
> >  
> >  	/* clear the whole window, note the arg is in kernel pages */
> > @@ -793,24 +782,44 @@ static void remove_ddw(struct device_node *np, bool remove_prop)
> >  		1ULL << (be32_to_cpu(dwp->window_shift) - PAGE_SHIFT), dwp);
> >  	if (ret)
> >  		pr_warn("%pOF failed to clear tces in window.\n",
> > -			np);
> > +			pdn);
> >  	else
> >  		pr_debug("%pOF successfully cleared tces in window.\n",
> > -			 np);
> > +			 pdn);
> >  
> >  	ret = rtas_call(ddw_avail[2], 1, 1, NULL, liobn);
> >  	if (ret)
> >  		pr_warn("%pOF: failed to remove direct window: rtas returned "
> >  			"%d to ibm,remove-pe-dma-window(%x) %llx\n",
> > -			np, ret, ddw_avail[2], liobn);
> > +			pdn, ret, ddw_avail[2], liobn);
> >  	else
> >  		pr_debug("%pOF: successfully removed direct window: rtas returned "
> >  			"%d to ibm,remove-pe-dma-window(%x) %llx\n",
> > -			np, ret, ddw_avail[2], liobn);
> > +			pdn, ret, ddw_avail[2], liobn);
> > +}
> > +
> > +static void remove_ddw(struct device_node *np, bool remove_prop)
> > +{
> > +	struct property *win;
> > +	u32 ddw_avail[3];
> > +	int ret = 0;
> > +
> > +	ret = of_property_read_u32_array(np, "ibm,ddw-applicable",
> > +					 &ddw_avail[0], 3);
> > +	if (ret)
> > +		return;
> > +
> > +	win = of_find_property(np, DIRECT64_PROPNAME, NULL);
> > +	if (!win)
> > +		return;
> > +
> > +	if (win->length >= sizeof(struct dynamic_dma_window_prop))
> 
> Any good reason not to make it "=="? Is there something optional or we
> expect extension (which may not grow from the end but may add cells in
> between). Thanks,

Well, it comes from the old behavior of remove_ddw():
-	if (ret || win64->length < sizeof(*dwp))
-		goto delprop;

As I reversed the logic from 'if (test) go out' to 'if (!test) do
stuff', I also reversed (a < b) to !(a < b) => (a >= b).

I have no problem changing that to '==', but it will produce a
different behavior than before. 

> 
> 
> > +		remove_dma_window(np, ddw_avail, win);
> > +
> > +	if (!remove_prop)
> > +		return;
> >  
> > -delprop:
> > -	if (remove_prop)
> > -		ret = of_remove_property(np, win64);
> > +	ret = of_remove_property(np, win);
> >  	if (ret)
> >  		pr_warn("%pOF: failed to remove direct window property: %d\n",
> >  			np, ret);
> > 

Best regards,
Leonardo