> -----Original Message----- > From: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx> > Sent: Monday, June 12, 2023 4:23 AM > To: linux-wireless@xxxxxxxxxxxxxxx; Ping-Ke Shih <pkshih@xxxxxxxxxxx> > Cc: Lukas F. Hartmann <lukas@xxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; tony0620emma@xxxxxxxxx; > jernej.skrabec@xxxxxxxxx > Subject: wifi: rtw88: question about SDIO RX aggregation limiting > > Hello Ping-Ke, > > certain Amlogic SDIO host controllers have a limit of > receiving/transmitting at most 1536 bytes at a time. > It turns out that rtw_sdio_enable_rx_aggregation() from rtw88/sdio.c > is not taking this into account currently. > For any RX buffer that is bigger than 1536 bytes (which can happen due > to RX aggregation) we're unable to do any processing on the host side > because all bytes beyond the 1536 bytes mark are lost. > > Lukas found that limiting BIT_RXDMA_AGG_PG_TH to 0x6 makes his > RTL8822CS work on the affected Amlogic SoCs. > > My question now is: how can we properly limit BIT_RXDMA_AGG_PG_TH > without hard-coding a one-fits-all value (which may reduce > performance)? > > Initially I thought that we could just calculate it: > host_max_pages = mmc_host->max_req_size / rtwdev->chip->page_size > max_req_size for the affected controller is 1536 and chip->page_size > is 128, so the result would be 12 (I thought it would be close to this > number, maybe +/-1). > Unfortunately this doesn't fix the issue and for his board > BIT_RXDMA_AGG_PG_TH the limit is 6 or 7. > > If you could describe how BIT_RXDMA_AGG_PG_TH generally works I can > come up with the algorithm to calculate the limit on my own (at least > I hope so). > Lukas has been very patient with testing so far and I understood that > he's willing to test further patches if we think that it fixes the > rtw88 driver issue he's seeing. > The unit of BIT_RXDMA_AGG_PG_TH is 1k bytes, so I think you can set mmc_host->max_req_size/1024. I wonder why 0x6 works on Amlogic SoCs. Could you or Lukas compare performance between the settings of 0x1 and 0x6? Ping-Ke
