Messages in this thread | | | Subject | Re: [PATCH net 1/2] r8152: fix the sw rx checksum is unavailable | From | Mark Lord <> | Date | Thu, 24 Nov 2016 07:31:17 -0500 |
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On 16-11-23 02:29 PM, Mark Lord wrote: > On 16-11-23 10:12 AM, Hayes Wang wrote: >> Mark Lord [mlord@pobox.com] >> [...] >>> What does this code do: >> >>>> static void r8153_set_rx_early_size(struct r8152 *tp) >>>> { >>>> u32 mtu = tp->netdev->mtu; >>>> u32 ocp_data = (agg_buf_sz - mtu - VLAN_ETH_HLEN - VLAN_HLEN) / 4; >>>> >>>> ocp_write_word(tp, MCU_TYPE_USB, USB_RX_EARLY_SIZE, ocp_data); >>>> } >> >> This only works for RTL8153. However, what you use is RTL8152. >> It is like delay completion. It is used to reduce the loading of CPU >> by letting a transfer contain more data to reduce the number of >> transfers. >> >>> How is ocp_data used by the hardware? >>> Shouldn't the calculation also include sizeof(rx_desc) in there somewhere? >> >> The algorithm is from our hw engineers, and it should be >> >> (agg_buf_sz - packet size) / 8 >> >> You could refer to commit a59e6d815226 ("r8152: correct the rx early size"). > > Thanks. > > Right now I am working quite hard trying to narrow things down exactly. > You are correct that the driver does appear to be careful about accesses > beyond the filled portion of a URB buffer -- for some reason I thought > the original driver had issues there, but looking again it does not seem to. > > One idea that is now looking more likely: > Things could be suffering from speculative CPU accesses to RAM > (the system here has non-coherent d-cache/RAM). > This could incorrectly pre-load data from adjacent URB buffers > into the d-cache, creating coherency issues. I am testing now > with cacheline-sized guard zones between the buffers to see if > that is the issue or not.
Nope. Guard zones did not fix it, so it's probably not a prefetch issue. Oddly, adding a couple of memory barriers to specific places in the driver does help, A LOT. Still not 100%, but it did pass 1800 reboot tests over night with only three bad rx_desc's reported.
That's a new record here for the driver using kmalloc'd buffers, and put reliability on par with using non-cacheable buffers.
Any way we look at it though, the chip/driver are simply unreliable, and relying upon hardware checksums (which fail due to the driver looking at garbage rather than the checksum bits) leads to data corruption.
Cheers
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