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

[Lokesh Vutla]

On Sunday 02 September 2018 11:19 PM, Alexander Graf wrote:
> 
> 
>> Am 02.09.2018 um 18:04 schrieb Vagrant Cascadian <vagrant at debian.org>:
>>
>>> 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.
> 
> What I'm trying to say is that we probably want to make phys_addr_t be u64 when CONFIG_LPAE is set.

That's right. Enabling PHYS_64BIT should be sufficient. Based on this
phys_addr_t should be set to u32 or u64. arm already does that[1].

[1]
http://git.denx.de/?p=u-boot.git;a=blob;f=arch/arm/include/asm/types.h;h=9af7353f0866f05dbe298a603d52d90e9c8e6d28;hb=HEAD


Thanks and regards,
Lokesh