Hi, On 29/03/18 10:37, Maxime Ripard wrote: > On Wed, Mar 28, 2018 at 07:31:51PM +0800, Icenowy Zheng wrote: >> 于 2018年3月28日 GMT+08:00 下午7:28:07, Maxime Ripard <[email protected]> >> 写到: >>> On Mon, Mar 26, 2018 at 03:11:04PM +0800, Icenowy Zheng wrote: >>>> >>>> >>>> 于 2018年3月26日 GMT+08:00 下午3:06:33, Maxime Ripard >>> <[email protected]> 写到: >>>>> On Fri, Mar 23, 2018 at 05:41:43PM +0800, Icenowy Zheng wrote: >>>>>> >>>>>> >>>>>> 于 2018年3月23日 GMT+08:00 下午5:40:41, Maxime Ripard >>>>> <[email protected]> 写到: >>>>>>> On Fri, Mar 23, 2018 at 04:18:56PM +0800, Icenowy Zheng wrote: >>>>>>>> The get_ram_size() function in U-Boot can only deal with memory >>>>> size >>>>>>>> smaller than 2GiB. To enable the support of 3GiB DRAM on newer >>>>> 64-bit >>>>>>>> SoCs, an alternative way to detect DRAM size is needed. >>>>>>> >>>>>>> Why not just fixing get_ram_size then? >>>>>> >>>>>> Even if it's fixed it won't support 3GiB DRAM at all. >>>>> >>>>> Why? >>>> >>>> It has an assumption that the size is pow of 2. >>> >>> I guess this would be fixable too? (or one could create a variant >>> without that assumption). >> >> I don't think its principle allows such kind of fix, as it just >> checks writing then reading at some offset that is pow if 2. > > You could do have a bunch of algorithm actually. One would be to write > the address in memory and try to detect where exactly it starts to > loop. > > You could do a bisection in the opposite direction once you settled > for the upper limit (so you would have for example a workable 2G, a > non-workable 4G, and then you try intervals that you always divide by > two, so testing then 3G (that works), then halfway between 3G and 4G, > etc. > >> For hacking it, see my implementation in v1, which assumes the >> only size supported bigger than 2GiB is 3GiB (which is >> acceptable on sunxi, but might not work on other platforms). >> >> As Andre said, that function has another big problem -- it detects >> memory with writing to it. This is risky. > > How is it risky when it's done by the SPL?
Originally that was my confusion as well: It's not the SPL calling that function. The DRAM controller init function in there knows very precisely how much DRAM we have, but we don't communicate this to U-Boot proper. So U-Boot *proper* goes ahead and probes the DRAM. This means it could step into secure memory, for instance. On sunxi64 we have the ATF running between SPL and U-Boot, also all kind of secure payloads could already have been registered. So I wonder if it would be easier to somehow pass on this *one* word of information between SPL and U-Boot proper to avoid calling this function altogether? Cheers, Andre. _______________________________________________ U-Boot mailing list [email protected] https://lists.denx.de/listinfo/u-boot
