linux-kernel - Re: [PATCH v2 2/6] powerpc/pseries/iommu: Update call to ibm,query-pe-dma-windows

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Message-ID: <8f4c405363e4cd2a5a113f2a9a3f11a575d2947a.camel@gmail.com>
Date:   Wed, 01 Jul 2020 21:28:40 -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 v2 2/6] powerpc/pseries/iommu: Update call to
 ibm,query-pe-dma-windows

On Thu, 2020-07-02 at 10:18 +1000, Alexey Kardashevskiy wrote:
> 
> On 02/07/2020 00:04, Leonardo Bras wrote:
> > On Wed, 2020-07-01 at 18:17 +1000, Alexey Kardashevskiy wrote:
> > > > +#define DDW_EXT_SIZE		0
> > > > +#define DDW_EXT_RESET_DMA_WIN	1
> > > > +#define DDW_EXT_QUERY_OUT_SIZE	2
> > > 
> > > #define DDW_EXT_LAST (DDW_EXT_QUERY_OUT_SIZE + 1)
> > > ...
> > > 
> > > 
> > > > +
> > > >  static struct iommu_table_group *iommu_pseries_alloc_group(int node)
> > > >  {
> > > >  	struct iommu_table_group *table_group;
> > > > @@ -339,7 +343,7 @@ struct direct_window {
> > > >  /* Dynamic DMA Window support */
> > > >  struct ddw_query_response {
> > > >  	u32 windows_available;
> > > > -	u32 largest_available_block;
> > > > +	u64 largest_available_block;
> > > >  	u32 page_size;
> > > >  	u32 migration_capable;
> > > >  };
> > > > @@ -875,13 +879,29 @@ static int find_existing_ddw_windows(void)
> > > >  machine_arch_initcall(pseries, find_existing_ddw_windows);
> > > >  
> > > >  static int query_ddw(struct pci_dev *dev, const u32 *ddw_avail,
> > > > -			struct ddw_query_response *query)
> > > > +		     struct ddw_query_response *query,
> > > > +		     struct device_node *parent)
> > > >  {
> > > >  	struct device_node *dn;
> > > >  	struct pci_dn *pdn;
> > > > -	u32 cfg_addr;
> > > > +	u32 cfg_addr, query_out[5], ddw_ext[DDW_EXT_QUERY_OUT_SIZE + 1];
> > > 
> > > ... and use DDW_EXT_LAST here.
> > 
> > Because of the growing nature of ddw-extensions, I intentionally let
> > this be (DDW_EXT_QUERY_OUT_SIZE + 1). If we create a DDW_EXT_LAST, it
> > will be incremented in the future if more extensions come to exist.
> > 
> > I mean, I previously saw no reason for allocating space for extensions
> > after the desired one, as they won't be used here.
> 
> Ah, my bad, you're right.
> 
> 
> > > 
> > > >  	u64 buid;
> > > > -	int ret;
> > > > +	int ret, out_sz;
> > > > +
> > > > +	/*
> > > > +	 * From LoPAR level 2.8, "ibm,ddw-extensions" index 3 can rule how many
> > > > +	 * output parameters ibm,query-pe-dma-windows will have, ranging from
> > > > +	 * 5 to 6.
> > > > +	 */
> > > > +
> > > > +	ret = of_property_read_u32_array(parent, "ibm,ddw-extensions",
> > > > +					 &ddw_ext[0],
> > > > +					 DDW_EXT_QUERY_OUT_SIZE + 1);
> > 
> > In this case, I made sure not to cross (DDW_EXT_QUERY_OUT_SIZE + 1)
> > while reading the extensions from the property.
> > 
> > What do you think about it? 
> 
> I think you want something like:
> 
> static inline int ddw_read_ext(const struct device_node *np, int extnum,
> u32 *ret)
> {
> retun of_property_read_u32_index(np, "ibm,ddw-extensions", extnum + 1, ret);
> }
> 
> These "+1"'s all over the place are confusing.

That's a great idea!

I was not aware it was possible to read a single value[index] directly
from the property, but it makes total sense to use it.

Thank you!