On Thu, Feb 20, 2020 at 05:07:00PM +0100, Enric Balletbo i Serra wrote: > Hi Prashant, > > Could you base your next series on top of [1]. Also, if you can give your > feedback and test those, would be much appreciated ;-) Sure Enric, I will attempt to rebase on top of [1] this week. I'll update you once this is done. Thanks! -Prashant > > BTW, I think you need to fix your sendmail as the series are not threaded and > appear as independent patches in patchwork, which is a bit hard to follow. > > Thanks, > Enric > > [1] https://lore.kernel.org/patchwork/cover/1197210/ > > > On 18/2/20 19:30, Prashant Malani wrote: > > Hi All, > > > > Just thought I'd ping this thread since it's been a week since the last > > email. > > > > On Mon, Feb 10, 2020 at 12:14:01PM -0800, Prashant Malani wrote: > >> Hi All (trimming most code parts of the thread for the sake of brevity), > >> > >> Thanks for listing the points Enric, Please see my notes inline: > >> > >> On Mon, Feb 10, 2020 at 3:03 AM Enric Balletbo i Serra > >> <enric.balletbo@xxxxxxxxxxxxx> wrote: > >>> > >>> Hi Gwendal, Prashant et all > >>> > >>> On 7/2/20 19:47, Gwendal Grignou wrote: > >>>> On Thu, Feb 6, 2020 at 10:50 AM Prashant Malani <pmalani@xxxxxxxxxxxx> wrote: > >>>>> > >>>>> Hi Enric, > >>>>> > >>>>> Thanks for taking a look at the patch. Please see my response inline: > >> .... > >>>>>>>> @@ -171,9 +162,11 @@ int cros_ec_motion_send_host_cmd(struct cros_ec_sensors_core_state *state, > >>>>>>>> > >>>>>>>> memcpy(state->msg->data, &state->param, sizeof(state->param)); > >>>>>>>> > >>>>>>>> - ret = cros_ec_cmd_xfer_status(state->ec, state->msg); > >>>>>>>> + ret = cros_ec_cmd_xfer(state->ec, state->msg); > >>>>>>>> if (ret < 0) > >>>>>>>> return ret; > >>>>>>>> + else if (state->msg->result != EC_RES_SUCCESS) > >>>>>>>> + return -EPROTO; > >>>>>>>> > >>>>>> > >>>>>> There is no way to use the new cros_ec_cmd here? > >>>> When the EC does not support sensor fifo, > >>>> cros_ec_motion_send_host_cmd() is on the data path. For instance, it > >>>> is called 2 times every 10ms by chrome to calculate the lid angle. I > >>>> would be reluctant to call malloc. Given it is well encapsulated into > >>>> the sensor stack. Does it make sense to call cros_ec_cmd_xfer > >>>> directly? > >>>> > >>> > >>> Thanks Gwendal for pointing this, it makes totally sense, and I suspect this can > >>> happen on other cases. > >>> > >>> Just to make clear, my concern is not about not using the new 'cros_ec_cmd' > >>> here, is about changing 'cros_ec_cmd_xfer_status' for 'cros_ec_cmd_xfer'. Also, > >>> my other concern is how useful is the new 'cros_ec_cmd' replacing what we have > >>> now if cannot replace all current uses. > >>> > >>> My points of view are this: > >>> > >>> * Actually we have cros_ec_cmd_xfer and cros_ec_cmd_xfer_status, use the second > >>> one is better, in fact, we tried to move all the cros_ec_cmd_xfer to the _status > >>> version in the past because makes the code and error handling cleaner. So I'm > >>> reticent to get back to use cros_ec_cmd_xfer instead of cros_ec_cmd_xfer_status. > >>> > >>> * The users of the cros-ec protocol sometimes they mallocing/freeing at runtime, > >>> and sometimes they don't. IMHO *non* mallocing/freeing is usually better, more > >>> efficient and faster. Would be nice to standardize this. > >> > >> I think we should look at latency (I am assuming that is one of the > >> concerns Gwendal was referring to). > >> We should certainly do more rigorous measurements, but I did a crude > >> measurement across a devm_kzalloc() used on one of the EC commands > >> inside platform/chrome for struct EC command: > >> - Used ktime_get_ns() to record time before and after the devm_kzalloc() > >> - Used ktime_sub to subtract the "after" and "before" values: > >> > >> struct cros_ec_command *msg; > >> int ret; > >> + ktime_t start, end, diff; > >> > >> + start = ktime_get_ns(); > >> msg = kzalloc(sizeof(*msg) + max(outsize, insize), GFP_KERNEL); > >> + end = ktime_get_ns(); > >> if (!msg) > >> return -ENOMEM; > >> > >> + diff = ktime_sub(end, start); > >> + printk("%s(): TEST: kzalloc took: %lld\n", __func__, ktime_to_ns(diff)); > >> > >> On an i5 1.6 GHz system, across 16 call measurements I got the > >> following latency values (in ns): > >> - Count, N:16 > >> - Average: 72.375 > >> - Std. Dev : 28.768 > >> - Max: 143 > >> - Min: 51 > >> > >> Are these values significant for the various call-sites? I think the > >> driver authors might be able to comment better there (unfortunately I > >> don't have enough context for each case). > >> Of course there will be other overhead (memcpy) but I think this is a > >> good starting point for the discussion. > >> (My apologies if this measurement method is incorrect/inaccurate.) > > > > Any thoughts / comments here? > > > > On an overall note, I think keeping cros_ec_cmd_xfer() and cros_ec_cmd() > > might be a good starting point. > > > > In this way, we are not introducing any extra function. Also, we can > > begin converting the cros_ec_cmd_xfer() use cases (a few call-sites may > > need to be investigated from a latency perspective). The > > cros_ec_cmd_xfer() conversions are better handled in separate patch > > series. > > > > Best regards, > > > > -Prashant > >> > >>> > >>> * If we want to introduce a new 'cros_ec_cmd', this should make the code cleaner > >>> and ideally should be the way we tell the users they should use to communicate > >>> with the cros-ec and not open coding constantly. Ideally, should be a > >>> replacement of all current 'cros_ec_cmd_xfer*' versions. > >> > >> As I mentioned previously, I think all calls of cros_ec_cmd_xfer() can > >> be converted to use cros_ec_cmd() (especially since the new API has a > >> *result pointer), > >> but I think it should be staged out a bit more (since cases like iio: > >> cros_ec driver require non-trivial refactoring which I think is better > >> in a patch/series). > >> > >>> > >>> * If 'cros_ec_cmd' *cannot* replace all the cases, it should be clear to the > >>> user in which cases he should use this function and in which cases shouldn't use > >>> this function. > >> > >> This seems like a good compromise, but my expectation is that if there > >> is a "fast" and "slow" version of the same functionality, developers > >> would be inclined to use the "fast" version always? > >> > >> > >>> * Finally, what pointed Gwendal, what's the best approach to send commands to > >>> the EC by default, is better use dynamic memory? or is better use the stack? is > >>> it always safe use the stack? is always efficient use allocated memory? > >>> > >>> As you can see I have a lot of questions still around, but taking in > >>> consideration that this will be an important change I think that makes sense > >>> spend some time discussing it. > >>> > >>> What do you think? > >>> > >>> Enric > >>> > >>> > >>>> Gwendal. > >>>>> > >>>>> I think it is doable. From looking at the code I felt the factors we > >>>>> need to be careful about are: > >>>>> - The function cros_ec_motion_send_host_cmd() is called from a few > >>>>> other files, each of which set up the struct cros_ec_command > >>>>> differently (reference: > >>>>> https://elixir.bootlin.com/linux/latest/ident/cros_ec_motion_send_host_cmd) > >>>>> - It is not clear to me how readability will be affected by making the > >>>>> change to cros_ec_cmd(). > >>>>> > >>>>> Due to the above two factors, but primarily because I wanted to avoid > >>>>> making such an involved large change in this 17 patch series, I > >>>>> reasoned it would be better to make the transition to cros_ec_cmd() > >>>>> for these files in a separate patch/series. > >>>>> My plan after this patch series is to work on this driver(perhaps we > >>>>> can eliminate cros_ec_motion_send_host_cmd() itself?), and then remove > >>>>> cros_ec_cmd_xfer() usage. > >>>>> > >>>>> WDYT? > >>>>> > >>>>> Best regards, > >>>>> > >>>>> > >>>>>> > >>>>>> > >>>>>>>> if (ret && > >>>>>>>> state->resp != (struct ec_response_motion_sense *)state->msg->data) > >>>>>>>
