[U-Boot] [PATCH 1/9] dm: allow 4GB of DRAM on 32bit systems

[Vagrant Cascadian]

On 2018-09-02, Alexander Graf <agraf at suse.de> wrote:
> On 02.08.18 23:31, Dr. Philipp Tomsich wrote:
>> 
>>> On 2 Aug 2018, at 22:36, Simon Glass <sjg at chromium.org> wrote:
>>>
>>> On 26 July 2018 at 07:59, Philipp Tomsich
>>> <philipp.tomsich at theobroma-systems.com <mailto:philipp.tomsich at theobroma-systems.com>> wrote:
>>>> Even on 32bit systems a full 4GB of DRAM may be installed and reported
>>>> by the DRAM controller.  Whether these 4GB are larger available
>>>> depends on the size/configuration of address decoding windows and
>>>> architectural features (e.g. consider a hypothetical architecture that
>>>> uses dedicated instructions to access the 'memory-mapped' peripheral
>>>> IO ranges).  In U-Boot, the available DRAM, as reported by the
>>>> device-model is independent of the accessible DRAM (i.e. adjusted top
>>>> and effective size).
>>>>
>>>> This was first reported against the RK3288, which may have 4GB DRAM
>>>> attached, but will have a small (e.g. 128MB) window not accessible due
>>>> to address decoding limitations.
>>>>
>>>> The solution is to increase the types used for storing the ram_size to
>>>> have at least 33 bits even on 32bit systems... i.e. we need to use a
>>>> u64 for these always (this was previously only the case for
>>>> PHYS_64BIT, which will have unwanted side-effects for 32bit systems
>>>> and would require more intrusive changes).
>>>>
>>>> This commit changes the size-field in 'struct ram' and the ram_size in
>>>> 'gd' to be a u64.
>>>>
>>>> Reported-by: Marty E. Plummer <hanetzer at startmail.com>
>>>> Signed-off-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
>>>> ---
>>>>
>>>> include/asm-generic/global_data.h | 2 +-
>>>> include/ram.h                     | 9 ++++++++-
>>>> 2 files changed, 9 insertions(+), 2 deletions(-)
>>>>
>>>
>>> Reviewed-by: Simon Glass <sjg at chromium.org <mailto:sjg at chromium.org>>
>>>
>>>> diff --git a/include/asm-generic/global_data.h b/include/asm-generic/global_data.h
>>>> index 0fd4900..f3d687c 100644
>>>> --- a/include/asm-generic/global_data.h
>>>> +++ b/include/asm-generic/global_data.h
>>>> @@ -55,7 +55,7 @@ typedef struct global_data {
>>>>        unsigned long ram_base;         /* Base address of RAM used by U-Boot */
>>>>        unsigned long ram_top;          /* Top address of RAM used by U-Boot */
>>>>        unsigned long relocaddr;        /* Start address of U-Boot in RAM */
>>>> -       phys_size_t ram_size;           /* RAM size */
>>>> +       u64 ram_size;                   /* RAM size */
>>>>        unsigned long mon_len;          /* monitor len */
>>>>        unsigned long irq_sp;           /* irq stack pointer */
>>>>        unsigned long start_addr_sp;    /* start_addr_stackpointer */
>>>> diff --git a/include/ram.h b/include/ram.h
>>>> index 67e22d7..1fe024f 100644
>>>> --- a/include/ram.h
>>>> +++ b/include/ram.h
>>>> @@ -9,7 +9,14 @@
>>>>
>>>> struct ram_info {
>>>>        phys_addr_t base;
>>>> -       size_t size;
>>>> +       /*
>>>> +        * We use a 64bit type for the size to correctly handle 32bit
>>>> +        * systems with 4GB of DRAM (which would overflow a 32bit type
>>>> +        * and read back as 0).  For 64bit systems, we assume (for now)
>>>
>>> forever :-)
>>>
>>>> +        * that they will always have less than 2^65 byte of DRAM
>>>> +        * installed. -- prt
>>>
>>> Is the prt your signature? I suggest dropping it.
>> 
>> In fact it is. But I’ll need to rewrite the entire comment anyway for the next
>> version of this series as there’s even more functions and places that the
>> memory size is stored in...
>> 
>>>
>>>> +        */
>>>> +       u64 size;
>
> With LPAE available in all modern ARM cores, shouldn't phys_addr_t just
> be u64? And then we'd probably want to use that throughout the code, right?

Quite a few currently supported boards do not support LPAE, e.g. imx6.


live well,
  vagrant
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