linux-kernel - Re: [PATCH] media: venus: firmware: Use of_reserved_mem

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Date:   Wed, 31 May 2023 11:23:22 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     Mukesh Ojha <quic_mojha@...cinc.com>
Cc:     Vikash Garodia <quic_vgarodia@...cinc.com>,
        Stanimir Varbanov <stanimir.k.varbanov@...il.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: venus: firmware: Use of_reserved_mem_lookup()

On Wed, May 31, 2023 at 01:15:26PM +0530, Mukesh Ojha wrote:
> 
> 
> 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@...00000 {
> > > 		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 ?
> 

Yes, when using of_reserved_mem_lookup() the allocated address is
available in rmem->base. If you have this patch applied then it should
be given to the TZ call as expected.

Thanks,
Stephan