On 3/15/2018 10:32 AM, Alexander Duyck wrote: > We tend to do something like: > update tx_buffer_info > update tx_desc > wmb() > point first tx_buffer_info next_to_watch value at last tx_desc > update next_to_use > notify device via writel > > We do it this way because we have to synchronize between the Tx > cleanup path and the hardware so we basically lump the two barriers > together. instead of invoking both a smp_wmb and a wmb. Now that I > look at the pseudocode though I wonder if we shouldn't move the > next_to_use update before the wmb, but that might be material for > another patch. Anyway, in the Tx cleanup path we should have an > smp_rmb() after we read the next_to_watch values so that we avoid > reading any of the other fields in the buffer_info if either the field > is NULL or the descriptor pointed to has not been written back. How do you feel about keeping wmb() very close to writel_relaxed() like this? update tx_buffer_info update tx_desc point first tx_buffer_info next_to_watch value at last tx_desc update next_to_use wmb() notify device via writel_relaxed() I'm afraid that if the order of wmb() and writel() is not very obvious or hidden in multiple functions, somebody can introduce a very nasty bug in the future. We also have to think about code maintenance. -- Sinan Kaya Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project. -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
