Re: [PATCH] media: venus: firmware: Use of_reserved_mem_lookup()

[Mukesh Ojha]

On 5/31/2023 1:04 PM, Vikash Garodia wrote:
> On 5/31/2023 12:26 PM, Stephan Gerhold wrote:
> > On Wed, May 31, 2023 at 11:36:52AM +0530, Vikash Garodia wrote:
> > > On 5/29/2023 11:46 PM, Stephan Gerhold wrote:
> > > > Reserved memory can be either looked up using the generic function
> > > > of_address_to_resource() or using the special of_reserved_mem_lookup().
> > > > The latter has the advantage that it ensures that the referenced memory
> > > > region was really reserved and is not e.g. status = "disabled".
> > > >
> > > > of_reserved_mem also supports allocating reserved memory dynamically at
> > > > boot time. This works only when using of_reserved_mem_lookup() since
> > > > there won't be a fixed address in the device tree.
> > > IIUC, this would avoid precomputing the hard range for different firmware
> > > regions and also make it more flexible to adjust the sizes, if anyone wants a
> > > bigger size later.
> > > Incase a specific firmware needs a dedicate start address, do we have an option
> > > to specify the same ?
> >
> > If you want a specific start address (or in other words: a fixed base
> > address) then you should continue using static reservation for that
> > component. You can mix static and dynamic reservations. The static ones
> > (with fixed addresses) will be reserved first, then the dynamic ones
> > will be allocated from the free space.
> >
> > I have this example for one device in my proposal at [1]:
> >
> > 	/* Firmware must be loaded at address 0x8b600000 */
> > 	wcnss_mem: wcnss@8b600000 {
> > 		reg = <0x8b600000 0x600000>;
> > 		no-map;
> > 	};
> > 	/* Firmware can be loaded anywhere with 1 MiB alignment */
> > 	venus_mem: venus {
> > 		size = <0x500000>;
> > 		alignment = <0x100000>;
> > 		no-map;
> > 	};
> >
> > The wcnss_mem will be always at 0x8b600000, but the venus_mem can be
> > loaded somewhere around that. If only certain regions need a fixed
> > address this still provides the flexibility to change sizes more easily.
> >
> > Does that answer your question? I wasn't sure what exactly you mean with
> > a "dedicated start address". :)
> Yes, it clarified the need if any subsystem wants a specific start address.
>
> One more thing, lets say, we keep it dynamic allocation and at the same time we
> need to pass the start address to TZ call in [1]. How do we get that allocated
> address so as to pass in [1] ?

+	*mem_phys = rmem->base;

It will provide the start, is not it ?

-- Mukesh

> Thanks,
> Vikash
>
> [1]:
> https://elixir.bootlin.com/linux/v6.4-rc4/source/drivers/soc/qcom/mdt_loader.c#L249